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sources/tech/20230116 AI- Introduction to Keras and Our First Data Set.md
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[#]: subject: "AI: Introduction to Keras and Our First Data Set"
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[#]: via: "https://www.opensourceforu.com/2023/01/ai-introduction-to-keras-and-our-first-data-set/"
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[#]: author: "Deepu Benson https://www.opensourceforu.com/author/deepu-benson/"
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[#]: collector: "lujun9972/lctt-scripts-1700446145"
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[#]: translator: "toknow-gh"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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AI: Introduction to Keras and Our First Data Set
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======
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<https://www.opensourceforu.com/wp-content/uploads/2022/11/AI-Keras-1.jpg>
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_In the last article in this series on AI and machine learning, we learned to use Anaconda. We also tried to strengthen our knowledge of probability, a task we will continue in this article. We will discuss seaborn and Keras, and further explore Pandas and TensorFlow in this sixth article in the AI series._
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Let us begin by increasing our theoretical knowledge of AI and machine learning. We all know that AI, machine learning, data science, deep learning, etc, are the trending topics in computer science today. However, there are other topics trending in this domain too such as blockchain, IoT (Internet of Things), quantum computing, etc. So do the advances in the field of AI affect any of these technologies in a positive way?
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First, let us discuss blockchain. According to Wikipedia, “A blockchain is a type of distributed ledger technology that consists of a growing list of records, called blocks, that are securely linked together using cryptography.” At a casual glance it looks as if AI and blockchain are two independent technologies advancing at a very high pace at the same time in history. But surprisingly, this is not the case. The buzzword associated with blockchain is integrity and the buzzword associated with AI is data. We give massive amounts of data to AI based applications to process. Though the results produced by many of these applications are stunning, how do we trust them? This raises the need for explainable AI, which can give certain guarantees so that end users can trust the results provided by AI based applications. Many experts believe that blockchain technologies can be used to increase the trustworthiness of decisions made by AI based software. On the other hand, smart contracts (which are part of blockchain technology) can benefit from AI based verification. Notice that, in essence, smart contracts and AI often lead to decision making. Thus, we can safely conclude that the advances in AI will positively affect blockchain technology and vice versa.
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Now, let us discuss how AI and IoT impact each other. In the earlier days, IoT devices often did not have large processing power or battery backup. This made the deployment of machine learning based software, which requires large processing power, infeasible in many IoT devices. At that point in time, only rule-based AI software was being deployed in most IoT devices. The advantage with rule-based AI is that it is simple and requires relatively less processing power. However, nowadays, IoT devices are equipped with more processing power and can run powerful machine learning software. The advanced driver-assistance system developed by Tesla, called Tesla Autopilot, is an excellent example for the blending of IoT and AI. Thus, here again, AI and IoT are positively affecting each other’s development.
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Finally, let us try to understand how AI and quantum computing are impacting each other. Even though quantum computing is still in its infancy, quantum machine learning (QML) is taken very seriously. Quantum machine learning is based on two concepts: quantum data and hybrid quantum-classical models. Quantum data is the data generated by a quantum computer. Quantum neural networks (QNNs) are used to model quantum computational models. A powerful tool for developing quantum computational models is TensorFlow Quantum, a library for hybrid quantum-classical machine learning. The presence of this and many other tools indicates that more and more quantum computing based AI solutions will be available in the near future.
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### Introduction to seaborn
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Now let us learn to use seaborn. Seaborn is a Python data visualisation library based on Matplotlib. It provides functions for drawing visually appealing statistical images. Seaborn can be installed easily by using Anaconda Navigator, as explained in the previous article in this series. I have used the batting records in T20 international cricket from the website ESPNcricinfo to create a CSV (comma-separated values) file called T20.csv, which contains the following 15 columns: Player name, Career span, Matches, Innings, Not out, Total runs, Highest score, Average, Balls faced, Strike rate, Centuries, Fifties, Ducks, Number of 4s scored, and Number of 6s scored. We will use the library called Pandas to read this CSV file. Remember that we have already familiarised ourselves with Pandas. Now, consider the program shown in Figure 1.
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![Figure 1: A simple example for seaborn][1]
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Let us try to understand the working of the program. Lines 1 and 2 import the packages Pandas and seaborn. Line 3 reads the CSV file called T20.csv from the working directory of JupyterLab. Line 4 prints the metadata and the first line of data. Figure 1 shows this line, which displays the batting record of Virat Kohli, the highest run scorer in T20 international cricket matches. Line 5 stores the metadata and the first five rows of data in the CSV file T20.csv to another CSV file called Best5.csv. On execution of the code, you will see this file created in the working directory of JupyterLab. Line 6 sorts the CSV file in ascending order based on the column ‘100’ (which contains the number of centuries scored by each batsman) and stores the details of the top 10 century scorers into a CSV file called Highest100.csv. This file will also be stored in the working directory of JupyterLab. Finally, Line 7 extracts details of columns 5 and 7 (total runs scored and average, respectively) and generates a scatter plot. Figure 2 shows this scatter plot generated by the program on execution.
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![Figure 2: A scatter plot with seaborn][2]
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Now add the following line of code at the end of the program and run it again.
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```
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sns.kdeplot(data=df.iloc[:, [5, 7]].head(50), x=’Ave’, y=’Runs’)
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```
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This draws a KDE plot, in addition to the scatter plot, of the data obtained from columns 5 and 7. The function kdeplot( ) gives a Kernel Distribution Estimation Plot, which depicts the probability density function of the continuous or non-parametric data variables. This definition may not give you any idea about the actual operation that will be performed by the function kdeplot( ). Figure 3 shows the KDE plot and scatter plot being drawn on a single image. From this figure, we can observe that data points drawn by the scatter plot are grouped into clusters by the KDE plot. Notice that there are a lot of other plotting functions also provided by seaborn. In the program we have discussed now, replace Line 7 with the lines of code (one line at a time) shown below, and execute the program again. You will see plots with varying styles. Explore the other plotting functions offered by seaborn and choose the one that suits your need the most.
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![Figure 3: A KDE plot with seaborn][3]
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```
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sns.histplot(data=df.iloc[:, [5, 7]].head(50), x=’Ave’, y=’Runs’)
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sns.rugplot(data=df.iloc[:, [5, 7]].head(50), x=’Ave’, y=’Runs’)
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```
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### More on probability
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Now, let us learn some more topics in probability. In one of the previous articles in this series, we saw how a normal distribution can be used to model real world scenarios. But normal distribution is just one among the many important probability distributions. Consider the program shown in Figure 4, which plots three probability distributions.
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![Figure 4: Program for probability distributions][4]
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Now, let us try to understand the program. Line 1 imports the random module of NumPy. Lines 2 and 3 import libraries Matplotlib and seaborn for plotting. Line 5 generates a binomial distribution with parameters n (number of trials) and p (probability of success).
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Binomial distribution is a discrete probability distribution, which gives the number of successes in a sequence of n independent experiments. The third parameter called size decides the shape of the output. Line 6 plots the histogram of the data generated. Notice that a KDE plot is also plotted because the parameter kde is set as true. The third parameter colour decides the colour of the plot, which in this case is red (‘r’). Line 7 generates a Poisson distribution (named after the French mathematician Siméon Denis Poisson). The Poisson distribution is a discrete probability distribution which gives the limit of the binomial distribution. The parameter lam sets the expected number of events occurring in a fixed-time interval. Here also the parameter size decides the shape of the output. Line 8 plots the data generated as a histogram in green. Line 9 generates an exponential distribution with a size of 1000. Line 10 plots the data generated as a histogram in blue. Finally, Line 11 displays all the plots generated. Figure 5 shows the three probability distributions plotted on execution of the program. The random module of NumPy offers a large number of other probability distributions like Dirichlet distribution, Gamma distribution, geometric distribution, Laplace distribution, etc. It would be really rewarding if you could work and get familiarised with more of them.
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![Figure 5: Plots of probability distributions][5]
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Now, let us learn about linear regression. Linear regression analysis can be used to predict the value of a variable based on the value of another variable. One of the important applications of linear regression is data fitting. Linear regression is very important because of its simplicity. The supervised learning paradigm of machine learning is actually another name for regression modelling. Thus, linear regression can be considered as an important machine learning strategy. This learning paradigm is often called statistical learning by statisticians. Both NumPy and SciPy offer functions for performing linear regression. Since linear regression is an important operation in machine learning, we will see examples involving both NumPy and SciPy. Now, consider the program shown in Figure 6.
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![Figure 6: Linear regression with NumPy][6]
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The program uses NumPy to perform linear regression. First, let us try to understand the working of this program. Lines 1 and 2 import NumPy and Matplotlib. Lines 4 and 5 initialise the variables a and b for data generation. Line 6 uses the function linspace( ) to generate evenly spaced numbers over the specified interval of 0 and 1. In this case 100 such numbers are generated. Line 7 generates values in the array y by using the values in the array x. The function randn( ) returns samples from the standard normal distribution. These values, together with the values provided by the variables a, b, and array x, are used to generate the values in the array y. Line 8 generates a scatter plot by using the values in the arrays x and y. Figure 7 shows this scatter plot. The hundred data points are marked in red. Line 9 uses the function polyfit( ) to perform a least squares polynomial fit. It is one of the techniques used to perform linear regression. The function polyfit( ) takes for processing the arrays x and y, and a third parameter (in this case 1), which denotes the degree of the fitting polynomial. The function then returns the polynomial coefficients and they are stored in the array p. Line 10 uses the function polyval( ), which evaluates a polynomial at specific values. These values are stored in the array y_l. Line 11 plots the regression line in blue (Figure 7). Finally, Line 12 displays all the plots. This regression line can be used for making predictions about the possible (x, y) data pairs.
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![Figure 7: Linear regression scatter plot 1][7]
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Now, let us see how SciPy can be used to perform the same task. Consider the program shown in Figure 8.
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![Figure 8: Linear regression with SciPy][8]
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Let us try to understand the working of the program. Lines 1 and 2 import the libraries NumPy and Matplotlib. Line 3 imports the stats module from the library SciPy. Lines 4 to 8 are the same as the previous program and perform similar tasks. Line 9 uses the function linregress( ) offered by the stats module of SciPy, which can calculate a linear least-squares regression for two sets of measurements — in this case, the values in the arrays x and y. The function returns, in addition to other data, the slope and intercept of the regression line that is stored in the variables m and c, respectively. Line 10 uses the values of slope and intercept to generate the regression line. Line 11 plots the regression line in green. Finally, Line 12 displays all the plots. Figure 9 shows the image generated on execution of the program. The data points are displayed in yellow and the regression line is shown in green.
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![Figure 9: Linear regression scatter plot 2][9]
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In the last three articles in this series, we have tried to learn more and more concepts from probability and statistics. Though the treatment of the subject is in no way comprehensive, I think we have arrived at a good starting point and it is time to shift our focus to other matters of equal importance.
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### Introduction to Keras
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Now, let us learn to use Keras. Keras is used along with TensorFlow. Hence, let us begin by exploring TensorFlow a bit more. Consider the program shown in Figure 10. Though this program contains just four lines of code, this is our first encounter with neural networks in this series. Now, let us try to understand the working of the program. Line 1 imports the library TensorFlow. Line 2 creates a tensor called x. Lines 3 and 4 apply two activation functions called ReLU (Rectified Linear Unit) and Leaky ReLU, respectively, on the tensor x. In neural networks, the activation function of a node defines the output of that node given an input or set of inputs. ReLU activation function is an activation function defined as the positive part of its argument. The output of the code in Line 3 is shown in Figure 10. It can be observed that the negative values in the tensor x are replaced with zeros after applying the ReLU activation function. Leaky ReLU activation function is a modified version of the ReLU activation function. From the output of the code in Line 4 shown in Figure 10, it can be verified that positive values are retained as such, and 20 per cent of the negative values are retained on applying the Leaky ReLU activation function. Though we are moving on to discuss Keras, we will revisit this topic in the future to learn more about neural networks and activation functions.
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![Figure 10: TensorFlow for neural networks][10]
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Now, let us start using Keras. The installation of Keras can also be done very easily with Anaconda Navigator. Consider the program shown in Figure 11. We will use our first data set in this program. For the time being, we will only import and display sample data from the data set. But in the next article, we will use the same data set for training and testing our model, thus beginning the next phase in our journey to develop AI and machine learning based applications.
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![Figure 11: Our first data set][11]
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Now, let us try to understand the working of the program. Line 1 imports Keras. Line 2 imports the MNIST database of handwritten digits. It has a training data set of 60,000 samples and a test data set of 10,000 samples. Line 3 imports Matplotlib. Line 5 loads the data set. Lines 6 to 9 print the dimension and shape of the training data and the test data. Figure 12 shows the output of these lines of code. It can be seen that both the training data and the test data are three-dimensional. It can also be verified that there are 60,000 training images of 28 x 28 pixel quality and 10,000 test images of 28 x 28 pixel quality. Line 10 loads the 1234th training image. Lines 11 and 12 display this image. Figure 12 shows this handwritten image of the digit 3.
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![Figure 12: A sample from the data set][12]
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Now, it is time to wind-up our discussion. We are at the halfway mark of our journey through AI and machine learning. We have started discussing neural networks, a discussion we will continue in the next article. We have also come across our first data set with Keras. In the next article, we will continue discussing the use of Keras by training with this data set. We will also have our first interaction with scikit-learn, another powerful Python library for machine learning.
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--------------------------------------------------------------------------------
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via: https://www.opensourceforu.com/2023/01/ai-introduction-to-keras-and-our-first-data-set/
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作者：[Deepu Benson][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.opensourceforu.com/author/deepu-benson/
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[b]: https://github.com/lujun9972
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[1]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-1-A-simple-example-for-seaborn-1.png
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[2]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-2-A-scatter-plot-with-seaborn-1.png
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[3]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-3-A-KDE-plot-with-seaborn-1-590x415.png
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[4]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-4-Program-for-probability-distributions-1.png
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[5]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-5-Plots-of-probability-distributions-590x358.png
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[6]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-6-Linear-regression-with-NumPy-1.png
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[7]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-7-Linear-regression-scatter-plot-1-2.png
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[8]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-8-Linear-regression-with-SciPy.png
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[9]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-9-Linear-regression-scatter-plot-2-590x393.png
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[10]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-10-TensorFlow-for-Neural-Networks-2-590x121.png
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[11]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-11-Our-first-data-set-590x219.png
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[12]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-12-A-sample-from-the-data-set.png
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@ -0,0 +1,124 @@
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[#]: subject: "AI: Introduction to Keras and Our First Data Set"
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[#]: via: "https://www.opensourceforu.com/2023/01/ai-introduction-to-keras-and-our-first-data-set/"
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[#]: author: "Deepu Benson https://www.opensourceforu.com/author/deepu-benson/"
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[#]: collector: "lujun9972/lctt-scripts-1700446145"
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[#]: translator: "toknow-gh"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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人工智能教程（六）：Keras 和第一个数据集
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======
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<https://www.opensourceforu.com/wp-content/uploads/2022/11/AI-Keras-1.jpg>
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_在本系列的[上一篇文章](https://linux.cn/article-16526-1.html)中，我们学习了使用 Anaconda，加强了概率论的知识。在本文中我们将继续学习概率论的知识，学习使用 seaborn 和 Pandas 进行数据可视化，并进一步介绍 TensorFlow 和 Keras 的使用。_
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让我们从增长人工智能和机器学习的理论知识开始。众所周知人工智能、机器学习、数据科学、深度学习等是当今计算机科学的热门话题。然而，计算机科学还其他热门的话题，比如<ruby>区块链<rt>blockchain</rt></ruby>、<ruby>物联网<rt>Internet of Things</rt></ruby>（IoT）、<ruby>量子计算<rt>quantum computing</rt></ruby>等。那么，人工智能领域的发展是否会对这些技术产生积极的影响呢？
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首先，让我们讨论一下区块链。根据维基百科的定义，“区块链是一种分布式账本，它由不断增长的记录（称为<ruby>区块<rt>block</rt></ruby>）组成，这些记录使用加密技术安全地连接在一起。”乍一看，人工智能和区块链似乎是两个高速发展的独立技术。但令人惊讶的是，事实并非如此。区块链相关的行话是<ruby>完整性<rt>integrity</rt></ruby>，人工智能相关的行话是数据。我们将大量数据交给人工智能程序去处理。虽然这些应用程序产生了惊人的结果，但我们如何信任它们呢？这就提出了对可解释的人工智能的需求。它可以提供一定的保证，以便最终用户可以信任人工智能程序提供的结果。许多专家认为，区块链技术可以用来提高人工智能软件做出的决策的可信度。另一方面，<ruby>智能合约<rt>smart contracts</rt></ruby>（区块链技术的一部分）可以从人工智能的验证中受益。从本质上讲，智能合约和人工智能通常都是做决策。因此，人工智能的进步将对区块链技术产生积极影响，反之亦然。
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下面让我们讨论一下人工智能和物联网之间的影响。早期的物联网设备通常没有强大的处理能力或备用电池。这使得需要大量处理能力的机器学习的软件无法部署在物联网设备上。当时，大多数物联网设备中只部署了基于规则的人工智能软件。基于规则的人工智能的优势在于它很简单，需要相对较少的处理能力。如今的物联网设备具备更强大的处理能力，可以运行更强大的机器学习软件。特斯拉开发的高级驾驶辅助系统<ruby>特斯拉自动驾驶仪<rt>Tesla Autopilo</rt></ruby>是物联网与人工智能融合的典范。人工智能和物联网对彼此的发展产生了积极影响。
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最后，让我们讨论人工智能和量子计算是如何相互影响的。尽管量子计算仍处于起步阶段，但<ruby>量子机器学习<rt>quantum machine learning</rt></ruby>（QML）是其中非常重要的课题。量子机器学习基于两个概念：量子数据和量子-经典混合模型。量子数据是由量子计算机产生的数据。<ruby>量子神经网络<rt> quantum neural network</rt></ruby>（QNN）用于模拟量子计算模型。TensorFlow Quantum 是一个用于量子-经典混合机器学习的强大工具。这类工具的存在表明，在不久的将来将会有越来越多的基于量子计算的人工智能解决方案。
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### seaborn 入门
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seaborn 是一个基于 Matplotlib 的数据可视化 Python 库。用它能够绘制美观且信息丰富的统计图形。通过 Anaconda Navigator 可以轻松安装 seaborn。我用 ESPNcricinfo 网站上 T20 国际板球赛的击球记录，创建了一个名为 T20.csv 的 CSV（<ruby>逗号分隔值<rt>comma-separated value</rt></ruby>）文件，其中包含以下 15 列：球员姓名、职业生涯跨度、比赛场次、局数、未出局次数、总得分、最高得分、平均得分、面对球数、击球率、百分次数、五十分次数、零分次数、四分次数和六分次数。图 1 是使用 Pandas 库读取这个 CSV 文件的程序代码。我们已经在前面介绍过 Pandas 了。
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![图 1：使用 seaborn 的简单例子][1]
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下面逐行解释程序代码的作用。第 1 行和第 2 行导入 Pandas 和 seaborn 包。第 3 行从 JupyterLab 的工作目录中读取文件 T20.csv。第 4 行打印元数据和第一行数据。图 1 显示了这行数据，它显示了 T20 国际板球赛中得分最高的 Virat Kohli 的击球记录。第 5 行将元数据和 T20.csv 中的前五行数据保存到 Best5.csv 中。在执行该行代码时会在 JupyterLab 的工作目录中创建这个文件。第 6 行根据列百分次数按升序对 CSV 文件进行排序，并将前 10 名世纪得分手的详细信息存储到 Highest100.csv 中。该文件也将存储在 JupyterLab 的工作目录中。最后，第7行代码提取了第 5 列（总得分）和第 7 列（平均得分）的数据信息，并生成散点图。图 2 显示了程序在执行时生成的散点图。
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![图 2：seaborn 绘制的散点图][2]
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在程序末尾添加如下代码行并再次运行。
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```
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sns.kdeplot(data=df.iloc[:, [5, 7]].head(50), x=’Ave’, y=’Runs’)
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|
||||
```
|
||||
![图 3：使用 seaborn 绘制的核密度估计图][3]
|
||||
|
||||
这行代码调用 `kdeplot()` 函数绘制第 5 列和第 7 列数据的 <ruby>核密度估计<rt>Kernel Distribution Estimation</rt></ruby>（KDE）图。KDE 图可以描述连续或非参数数据变量的概率密度函数。这个定义可能无法让您了解函数 `kdeploy()` 将要执行的实际操作。图 3 是在单个图像上绘制的 KDE 图和散点图。从图中我们可以看到，散点图绘制的数据点被 KDE 图分组成簇。seaborn 还提供了许多其他绘图功能。在图 1 中程序的第 7 行分别替换为下面的的代码行（一次一行），并再次执行该程序，你会看到不同风格的绘图显示。探索 seaborn 提供的其他绘图功能，并选择最适合你需求的功能。
|
||||
|
||||
```
|
||||
|
||||
sns.histplot(data=df.iloc[:, [5, 7]].head(50), x=’Ave’, y=’Runs’)
|
||||
|
||||
sns.rugplot(data=df.iloc[:, [5, 7]].head(50), x=’Ave’, y=’Runs’)
|
||||
|
||||
```
|
||||
|
||||
### 更多概率论
|
||||
|
||||
在本系列之前的一篇文章中，我们看到可以用正态分布来对现实场景进行建模。但正态分布只是众多重要概率分布中的一种。图 4 中的程序绘制了三种概率分布。
|
||||
|
||||
![图 4：绘制多种概率分布的程序][4]
|
||||
|
||||
下面我来解释这个程序。第 1 行导入 NumPy 的 random 模块。第 2 行和第 3 行导入用于绘图的 Matplotlib 和 seaborn。第 5 行生成带有参数 `n`（试验次数）和 `p`（成功概率）的<ruby>二项分布<rt>binomial distribution</rt></ruby>数据。
|
||||
|
||||
二项分布是一种离散概率分布，它给出了在一系列 `n` 次独立实验中成功的数量。第三个参数 `size` 决定了输出的形状。第 6 行绘制生成的数据的直方图。由于参数 `kde=True`，它还会绘制 KDE 图。第三个参数 `color='r'` 表示绘图时使用红色。第 7 行生成一个泊松分布。泊松分布是一种离散概率分布，它给出了二项分布的极限。参数 `lam` 表示在固定时间间隔内发生预期事件的次数。这里的参数 `size` 也决定了输出的形状。第 8 行将生成的数据绘制为绿色的直方图。第 9 行生成大小为 1000 的指数分布。第 10 行将生成的数据绘制为蓝色的直方图。最后，第 11 绘制三个概率分布的所有图像（见图 5）。NumPy 的 random 模块提供了大量的其他概率分布，如 Dirichlet 分布、Gamma 分布、几何分布、拉普拉斯分布等。学习和熟悉它们将是非常值得的。
|
||||
|
||||
![图 5：概率分布的图像][5]
|
||||
|
||||
现在，让我们学习线性回归。使用线性回归分析可以根据一个变量来预测一个变量的值。线性回归的一个重要应用是数据拟合。线性回归非常重要，因为它很简单。机器学习中的监督学习范式实际上就是是回归建模。因此，线性回归可以被认为是一种重要的机器学习策略。这种学习范式通常被统计学家称为统计学习。线性回归是机器学习中的重要操作。NumPy 和 SciPy 都提供了线性回归的函数。下面我们展示使用 NumPy 和 SciPy 进行线性回归的示例。
|
||||
|
||||
![图 6：使用 NumPy 进行线性回归][6]
|
||||
|
||||
图 6 是使用 NumPy 进行线性回归的程序。第 1 行和第 2 行导入 NumPy 和 Matplotlib。第 4 行和第 5 行初始化变量 `a`和 `b`。第 6 行使用函数 `linspace()` 在 0 和 1 之间等间隔地生成 100 个数字。第 7 行使用变量 `a`、`b` 和数组 `x` 生成数组 `y` 中的值。函数 `randn()` 返回标准正态分布的数据。第 8 行将数组 `x` 和 `y` 中的值绘制成散点图（见图 7），图中的 100 个数据点用红色标记。第 9 行使用函数 `polyfit()` 执行称为<ruby>最小二乘多项式拟合<rt>least squares polynomial fit</rt></ruby>的线性回归技术。函数 `polyfit()` 的输入参数包括数组 `x` 和 `y`，以及第三个表示拟合多项式的阶数的参数，在本例中为 1，表示拟合一条直线。该函数的返回值是多项式的系数，代码中将其存储在数组 `p` 中。第 10 行使用函数 `polyval()` 对多项式求值，并将这些值存储在数组`y_l`中。第 11 行用蓝色绘制拟合得到的直线（见图 7）。最后，第 12 行显示所有的图像。可以用这条回归直线预测可能的 `(x, y)` 数据对。
|
||||
|
||||
![图 7：线性回归散点图 1][7]
|
||||
|
||||
图 8 是使用 SciPy 进行线性回归的程序代码。
|
||||
|
||||
![图 8：使用 SciPy 进行线性回归][8]
|
||||
|
||||
下面我解释一下这个程序的工作原理。第 1 行和第 2 行导入库 NumPy 和 Matplotlib。第 3 行从库 SciPy 导入 stats 模块。第 4 到 8 行与前面的程序执行类似的任务。第 9 行使用 SciPy 的 stats 模块的 `linregression()` 函数计算两组测量值的线性最小二乘回归——在在本例中是数组 `x` 和 `y` 中的值。该函数返回值中的 `m` 和 `c` 分别表示回归直线的<ruby>斜率<rt>slope</rt></ruby>和<ruby>截距<rt>intercept</rt></ruby>。第 10 行使用斜率和截距的值生成回归线。第 11 行用绿色绘制回归线。最后，第 12 行显示所有的图像（见图 9），其中数据点以黄色显示，回归线以绿色显示。
|
||||
|
||||
![图 9：线性回归散点图 2][9]
|
||||
|
||||
在本系列的前面几篇文章中，我们学习了概率和统计学的一些概念。尽管还不够全面的，但我认为这已经打下了一个良好的基础，现在是时候将注意力转移到其他同样重要的问题上了。
|
||||
|
||||
### Keras 简介
|
||||
|
||||
Keras 一般与 TensorFlow 一起使用。因此，我们先从使用 TensorFlow 开始。图 10 所示的程序虽然只包含四行代码，但确实构建了在本系列中的第一个神经网络。下面我来介绍它的工作原理。第 1 行导入库 TensorFlow。第 2 行创建了一个名为 `x` 的张量。第 3 行和第 4 行分别在张量 `x` 上应用 ReLU (Rectified Linear Unit，整流线性单元)和 Leaky ReLU 激活函数。在神经网络中，激活函数定义了节点的输出由输入计算出的规则。ReLU 激活函数是定义为 $Relu(x) = \max(0,x)$。第 3 行代码的输出如图 10 所示。可以观察到，在应用 ReLU 激活函数后，张量 `x` 中的负值被替换为零。Leaky ReLU 是 ReLU 激活函数的改进版本。从图 10 中的第 4 行代码的输出可以看出 Leaky ReLU 激活函数保留了全量的正值和 20% 的负值。在后面我们将会继续讨论 Keras，同时学习更多神经网络和激活函数的知识。
|
||||
|
||||
![图 10：使用 TensorFlow 实现的神经网络][10]
|
||||
|
||||
下面我们开始使用 Keras。Keras 的安装也可以通过 Anaconda Navigator 轻松完成。图 11 所示的程序导入了我们的第一个数据集并显示了其中的一个数据样本。在下一篇文章中，我们将使用这个数据集来训练和测试模型，从而开启我们开发人工智能和机器学习程序的下一个阶段。
|
||||
|
||||
![图 11：第一个数据集][11]
|
||||
|
||||
下面介绍这个程序的工作原理。第 1 行导入 Keras。第 2 行从 Keras 导入手写数字数据集 MNIST。它包含 6 万个训练样本和 1 万个测试样本。第 3 行导入 Matplotlib。第 5 行加载 MNIST 数据集。第 6 到 9 行打印训练集和测试集的维数和维度。图 12 显示了这些代码行的输出。可以看出，训练集和测试集都是三维的，所有数据样本的分辨率都是 28 × 28。第 10 行加载了第 1234 个训练图像。第 11 行和第 12 行显示这个图像。从图 12 可以看到它是数字 3 的手写图像。
|
||||
|
||||
![图 12：数据样例][12]
|
||||
|
||||
本文中我们开始涉及到神经网络，并通过 Keras 接触到了第一个数据集。在下一篇文章中，我们将继续讲解神经网络和 Keras，并通过使用该数据集训练自己的模型。我们还会遇到 scikit-learn, 它是另一个强大的机器学习Python 库 。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://www.opensourceforu.com/2023/01/ai-introduction-to-keras-and-our-first-data-set/
|
||||
|
||||
作者：[Deepu Benson][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[toknow-gh](https://github.com/toknow-gh)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://www.opensourceforu.com/author/deepu-benson/
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-1-A-simple-example-for-seaborn-1.png
|
||||
[2]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-2-A-scatter-plot-with-seaborn-1.png
|
||||
[3]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-3-A-KDE-plot-with-seaborn-1-590x415.png
|
||||
[4]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-4-Program-for-probability-distributions-1.png
|
||||
[5]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-5-Plots-of-probability-distributions-590x358.png
|
||||
[6]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-6-Linear-regression-with-NumPy-1.png
|
||||
[7]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-7-Linear-regression-scatter-plot-1-2.png
|
||||
[8]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-8-Linear-regression-with-SciPy.png
|
||||
[9]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-9-Linear-regression-scatter-plot-2-590x393.png
|
||||
[10]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-10-TensorFlow-for-Neural-Networks-2-590x121.png
|
||||
[11]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-11-Our-first-data-set-590x219.png
|
||||
[12]: https://www.opensourceforu.com/wp-content/uploads/2022/11/Figure-12-A-sample-from-the-data-set.png
|
||||
Loading…
Reference in New Issue
Block a user