diff --git a/sources/tech/20200602 Using pandas to plot data in Python.md b/sources/tech/20200602 Using pandas to plot data in Python.md new file mode 100644 index 0000000000..a75fc58ef5 --- /dev/null +++ b/sources/tech/20200602 Using pandas to plot data in Python.md @@ -0,0 +1,144 @@ +[#]: collector: (lujun9972) +[#]: translator: ( ) +[#]: reviewer: ( ) +[#]: publisher: ( ) +[#]: url: ( ) +[#]: subject: (Using pandas to plot data in Python) +[#]: via: (https://opensource.com/article/20/6/pandas-python) +[#]: author: (Shaun Taylor-Morgan https://opensource.com/users/shaun-taylor-morgan) + +Using pandas to plot data in Python +====== +Pandas is a hugely popular Python data manipulation library. Learn how +to use its API to plot data. +![Two pandas sitting in bamboo][1] + +In this series of articles on Python-based plotting libraries, we're going to have a conceptual look at plots using pandas, the hugely popular Python data manipulation library. Pandas is a standard tool in Python for scalably transforming data, and it has also become a popular way to [import and export from CSV and Excel formats][2]. + +On top of all that, it also contains a very nice plotting API. This is extremely convenient—you already have your data in a pandas DataFrame, so why not use the same library to plot it? + +In this series, we'll be making the same multi-bar plot in each library so we can compare how they work. The data we'll use is UK election results from 1966 to 2020: + +![Matplotlib UK election results][3] + +### Data that plots itself + +Before we go further, note that you may need to tune your Python environment to get this code to run, including the following.  + + * Running a recent version of Python (instructions for [Linux][4], [Mac][5], and [Windows][6]) + * Verify you're running a version of Python that works with these libraries + + + +The data is available online and can be imported using pandas: + + +``` +import pandas as pd +df = pd.read_csv('') +``` + +Now we're ready to go. We've seen some impressively simple APIs in this series of articles, but pandas has to take the crown. + +To plot a bar plot with a group for each party and `year` on the x-axis, I simply need to do this: + + +``` +import matplotlib.pyplot as plt +    +ax = df.plot.bar(x='year') +    +plt.show() +``` + +Four lines—definitely the tersest multi-bar plot we've created in this series. + +I’m using my data in [wide form][7], meaning there’s one column per political party: + + +``` +        year  conservative  labour  liberal  others +0       1966           253     364       12       1 +1       1970           330     287        6       7 +2   Feb 1974           297     301       14      18 +..       ...           ...     ...      ...     ... +12      2015           330     232        8      80 +13      2017           317     262       12      59 +14      2019           365     202       11      72 +``` + +This means pandas automatically knows how I want my bars grouped, and if I wanted them grouped differently, pandas makes it easy to [restructure my DataFrame][8]. + +As with [Seaborn][9], pandas' plotting feature is an abstraction on top of Matplotlib, which is why you call Matplotlib's `plt.show()` function to actually produce the plot. + +Here's what it looks like: + +![pandas unstyled data plot][10] + +Looks great, especially considering how easy it was! Let's style it to look just like the [Matplotlib][11] example. + +#### Styling it + +We can easily tweak the styling by accessing the underlying Matplotlib methods. + +Firstly, we can color our bars by passing a Matplotlib colormap into the plotting function: + + +``` +from matplotlib.colors import ListedColormap +cmap = ListedColormap(['#0343df', '#e50000', '#ffff14', '#929591']) +ax = df.plot.bar(x='year', colormap=cmap) +``` + +And we can set up axis labels and titles using the return value of the plotting function—it's simply a [Matplotlib `Axis` object][12]. + + +``` +ax.set_xlabel(None) +ax.set_ylabel('Seats') +ax.set_title('UK election results') +``` + +Here's what it looks like now: + +![pandas styled plot][13] + +That's pretty much identical to the Matplotlib version shown above but in 8 lines of code rather than 16! My inner [code golfer][14] is very pleased. + +### Abstractions must be escapable + +As with Seaborn, the ability to drop down and access Matplotlib APIs to do the detailed tweaking was really helpful. This is a great example of giving an abstraction [escape hatches][15] to make it powerful as well as simple. + +* * * + +_This article is based on [How to make plots using Pandas][16] on Anvil's blog and is reused with permission._ + +-------------------------------------------------------------------------------- + +via: https://opensource.com/article/20/6/pandas-python + +作者:[Shaun Taylor-Morgan][a] +选题:[lujun9972][b] +译者:[译者ID](https://github.com/译者ID) +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://opensource.com/users/shaun-taylor-morgan +[b]: https://github.com/lujun9972 +[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/panda.png?itok=0lJlct7O (Two pandas sitting in bamboo) +[2]: https://anvil.works/docs/data-tables/csv-and-excel +[3]: https://opensource.com/sites/default/files/uploads/matplotlib_2.png (Matplotlib UK election results) +[4]: https://opensource.com/article/20/4/install-python-linux +[5]: https://opensource.com/article/19/5/python-3-default-mac +[6]: https://opensource.com/article/19/8/how-install-python-windows +[7]: https://anvil.works/blog/tidy-data +[8]: https://anvil.works/blog/tidy-data#converting-between-long-and-wide-data-in-pandas +[9]: https://anvil.works/blog/plotting-in-seaborn +[10]: https://opensource.com/sites/default/files/uploads/pandas-unstyled.png (pandas unstyled data plot) +[11]: https://opensource.com/article/20/5/matplotlib-python +[12]: https://matplotlib.org/api/axis_api.html#axis-objects +[13]: https://opensource.com/sites/default/files/uploads/pandas_3.png (pandas styled plot) +[14]: https://en.wikipedia.org/wiki/Code_golf +[15]: https://anvil.works/blog/escape-hatches-and-ejector-seats +[16]: https://anvil.works/blog/plotting-in-pandas