diff --git a/CHANGELOG.md b/CHANGELOG.md
index f538bf5e7..ac6cf1c84 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
### Major Features and Improvements
* CASE construct (without aggregations)
+* rand() function added
### Bug Fixes and Other Changes
diff --git a/docs/user_technical/open-cypher.md b/docs/user_technical/open-cypher.md
index a27c936c7..323a728f8 100644
--- a/docs/user_technical/open-cypher.md
+++ b/docs/user_technical/open-cypher.md
@@ -440,6 +440,7 @@ functions.
`sign` | Applies the signum function to a given number and returns the result. The signum of positive numbers is 1, of negative -1 and for 0 returns 0.
`e` | Returns the base of the natural logarithm.
`pi` | Returns the constant *pi*.
+ `rand` | Returns a random floating point number between 0 (inclusive) and 1 (exclusive).
`startsWith` | Check if the first argument starts with the second.
`endsWith` | Check if the first argument ends with the second.
`contains` | Check if the first argument has an element which is equal to the second argument.
diff --git a/src/database/graph_db_accessor.cpp b/src/database/graph_db_accessor.cpp
index d8465c57a..cecee848f 100644
--- a/src/database/graph_db_accessor.cpp
+++ b/src/database/graph_db_accessor.cpp
@@ -9,7 +9,9 @@
#include "utils/on_scope_exit.hpp"
GraphDbAccessor::GraphDbAccessor(GraphDb &db)
- : db_(db), transaction_(db.tx_engine_.Begin()) {}
+ : db_(db), transaction_(db.tx_engine_.Begin()) {
+ pseudo_rand_gen_.seed(std::random_device()());
+}
GraphDbAccessor::~GraphDbAccessor() {
if (!commited_ && !aborted_) {
@@ -332,3 +334,5 @@ const std::string &GraphDbAccessor::PropertyName(
debug_assert(!commited_ && !aborted_, "Accessor committed or aborted");
return *property;
}
+
+double GraphDbAccessor::Rand() { return rand_dist_(pseudo_rand_gen_); }
diff --git a/src/database/graph_db_accessor.hpp b/src/database/graph_db_accessor.hpp
index edf156910..47bd958b2 100644
--- a/src/database/graph_db_accessor.hpp
+++ b/src/database/graph_db_accessor.hpp
@@ -6,6 +6,7 @@
#pragma once
#include <experimental/optional>
+#include <random>
#include "cppitertools/filter.hpp"
#include "cppitertools/imap.hpp"
@@ -552,6 +553,11 @@ class GraphDbAccessor {
if (!accessor.new_) accessor.new_ = accessor.vlist_->update(*transaction_);
}
+ /**
+ * Returns a uniformly random-generated number from the [0, 1) interval.
+ */
+ double Rand();
+
private:
/**
* Insert this vertex into corresponding label and label+property (if it
@@ -584,6 +590,7 @@ class GraphDbAccessor {
void UpdatePropertyIndex(const GraphDbTypes::Property &property,
const RecordAccessor<Vertex> &record_accessor,
const Vertex *const vertex);
+
GraphDb &db_;
/** The current transaction */
@@ -591,4 +598,8 @@ class GraphDbAccessor {
bool commited_{false};
bool aborted_{false};
+
+ // Random number generation stuff.
+ std::mt19937 pseudo_rand_gen_;
+ std::uniform_real_distribution<> rand_dist_{0, 1};
};
diff --git a/src/query/interpret/awesome_memgraph_functions.cpp b/src/query/interpret/awesome_memgraph_functions.cpp
index cbc49f648..304c5e499 100644
--- a/src/query/interpret/awesome_memgraph_functions.cpp
+++ b/src/query/interpret/awesome_memgraph_functions.cpp
@@ -453,6 +453,13 @@ TypedValue Pi(const std::vector<TypedValue> &args, GraphDbAccessor &) {
return M_PI;
}
+TypedValue Rand(const std::vector<TypedValue> &args, GraphDbAccessor &dba) {
+ if (args.size() != 0U) {
+ throw QueryRuntimeException("rand shouldn't be called with arguments");
+ }
+ return dba.Rand();
+}
+
template <bool (*Predicate)(const std::string &s1, const std::string &s2)>
TypedValue StringMatchOperator(const std::vector<TypedValue> &args,
GraphDbAccessor &) {
@@ -534,6 +541,7 @@ NameToFunction(const std::string &function_name) {
if (function_name == "SIGN") return Sign;
if (function_name == "E") return E;
if (function_name == "PI") return Pi;
+ if (function_name == "RAND") return Rand;
if (function_name == kStartsWith) return StartsWith;
if (function_name == kEndsWith) return EndsWith;
if (function_name == kContains) return Contains;
diff --git a/tests/qa/tck_engine/tests/memgraph_V1/features/functions.feature b/tests/qa/tck_engine/tests/memgraph_V1/features/functions.feature
index 5399c4ce6..3dc29b65f 100644
--- a/tests/qa/tck_engine/tests/memgraph_V1/features/functions.feature
+++ b/tests/qa/tck_engine/tests/memgraph_V1/features/functions.feature
@@ -616,6 +616,15 @@ Feature: Functions
| n |
| 3.141592653589793 |
+ Scenario: Rand test:
+ When executing query:
+ """
+ WITH rand() as r RETURN r >= 0.0 AND r < 1.0 as result
+ """
+ Then the result should be:
+ | result |
+ | true |
+
Scenario: All test 01:
When executing query:
"""
diff --git a/tests/unit/graph_db_accessor.cpp b/tests/unit/graph_db_accessor.cpp
index b99084761..083528e3c 100644
--- a/tests/unit/graph_db_accessor.cpp
+++ b/tests/unit/graph_db_accessor.cpp
@@ -352,6 +352,19 @@ TEST(GraphDbAccessorTest, Transfer) {
EXPECT_EQ(dba3->Transfer(e12)->PropsAt(prop).Value<int64_t>(), 12);
}
+TEST(GraphDbAccessorTest, Rand) {
+ Dbms dbms;
+ auto dba = dbms.active();
+
+ double a = dba->Rand();
+ EXPECT_GE(a, 0.0);
+ EXPECT_LT(a, 1.0);
+ double b = dba->Rand();
+ EXPECT_GE(b, 0.0);
+ EXPECT_LT(b, 1.0);
+ EXPECT_NE(a, b);
+}
+
int main(int argc, char **argv) {
::testing::InitGoogleTest(&argc, argv);
// ::testing::GTEST_FLAG(filter) = "*.DetachRemoveVertex";
diff --git a/tests/unit/query_expression_evaluator.cpp b/tests/unit/query_expression_evaluator.cpp
index 3abb26989..c9dbbf83a 100644
--- a/tests/unit/query_expression_evaluator.cpp
+++ b/tests/unit/query_expression_evaluator.cpp
@@ -1047,6 +1047,12 @@ TEST(ExpressionEvaluator, FunctionPi) {
ASSERT_DOUBLE_EQ(EvaluateFunction("PI", {}).Value<double>(), M_PI);
}
+TEST(ExpressionEvaluator, FunctionRand) {
+ ASSERT_THROW(EvaluateFunction("RAND", {1}), QueryRuntimeException);
+ ASSERT_GE(EvaluateFunction("RAND", {}).Value<double>(), 0.0);
+ ASSERT_LT(EvaluateFunction("RAND", {}).Value<double>(), 1.0);
+}
+
TEST(ExpressionEvaluator, FunctionStartsWith) {
EXPECT_THROW(EvaluateFunction(kStartsWith, {}), QueryRuntimeException);
EXPECT_TRUE(EvaluateFunction(kStartsWith, {"a", TypedValue::Null}).IsNull());