Add binary log expression.

Author: viirya

python/pyspark/sql/functions.py

@@ -143,7 +143,8 @@ def _():
     'atan2': 'Returns the angle theta from the conversion of rectangular coordinates (x, y) to' +
              'polar coordinates (r, theta).',
     'hypot': 'Computes `sqrt(a^2^ + b^2^)` without intermediate overflow or underflow.',
-    'pow': 'Returns the value of the first argument raised to the power of the second argument.'
+    'pow': 'Returns the value of the first argument raised to the power of the second argument.',
+    'logarithm': 'Returns the first argument-based logarithm of the second argument',
 }
 
 _window_functions = {

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala

@@ -122,6 +122,7 @@ object FunctionRegistry {
     expression[Tanh]("tanh"),
     expression[ToDegrees]("todegrees"),
     expression[ToRadians]("toradians"),
+    expression[Logarithm]("logarithm"),
 
     // aggregate functions
     expression[Average]("avg"),

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala

@@ -202,3 +202,14 @@ case class Pow(left: Expression, right: Expression)
       """
   }
 }
+
+case class Logarithm(left: Expression, right: Expression)
+  extends BinaryMathExpression((c1, c2) => math.log(c2) / math.log(c1), "LOG") {
+  override def genCode(ctx: CodeGenContext, ev: GeneratedExpressionCode): String = {
+    defineCodeGen(ctx, ev, (c1, c2) => s"java.lang.Math.log($c2) / java.lang.Math.log($c1)") + s"""
+      if (Double.valueOf(${ev.primitive}).isNaN()) {
+        ${ev.isNull} = true;
+      }
+      """
+  }
+}

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala

@@ -176,4 +176,8 @@ class MathFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper {
     testBinary(Atan2, math.atan2)
   }
 
+  test("binary log") {
+    testBinary(Logarithm, (c1, c2) => math.log(c2) / math.log(c1),
+      (1 to 20).map(v => (v * 0.1, v * 0.2)))
+  }
 }

sql/core/src/main/scala/org/apache/spark/sql/functions.scala

@@ -1299,6 +1299,70 @@ object functions {
    */
   def toRadians(columnName: String): Column = toRadians(Column(columnName))
 
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(l: Column, r: Column): Column = Logarithm(l.expr, r.expr)
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(l: Column, rightName: String): Column = logarithm(l, Column(rightName))
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(leftName: String, r: Column): Column = logarithm(Column(leftName), r)
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(leftName: String, rightName: String): Column =
+    logarithm(Column(leftName), Column(rightName))
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(l: Column, r: Double): Column = logarithm(l, lit(r).expr)
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(leftName: String, r: Double): Column = logarithm(Column(leftName), r)
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(l: Double, r: Column): Column = logarithm(lit(l).expr, r)
+
+  /**
+   * Returns the first argument-base logarithm of the second argument.
+   *
+   * @group math_funcs
+   * @since 1.4.0
+   */
+  def logarithm(l: Double, rightName: String): Column = logarithm(l, Column(rightName))
 
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