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[SPARK-8218][SQL] Binary log math function update. #6871

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[SPARK-8218][SQL] Binary log math function update. #6871

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[SPARK-8218][SQL] Binary log math function update.
rxin Jun 18, 2015
76fc8de
Fixed arg.
rxin Jun 18, 2015
ab51542
Use JVM log
rxin Jun 18, 2015
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13 changes: 9 additions & 4 deletions python/pyspark/sql/functions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -404,18 +404,23 @@ def when(condition, value):
return Column(jc)


@since(1.4)
def log(col, base=math.e):
@since(1.5)
def log(arg1, arg2=None):
"""Returns the first argument-based logarithm of the second argument.

>>> df.select(log(df.age, 10.0).alias('ten')).map(lambda l: str(l.ten)[:7]).collect()
If there is only one argument, then this takes the natural logarithm of the argument.

>>> df.select(log(10.0, df.age).alias('ten')).map(lambda l: str(l.ten)[:7]).collect()
['0.30102', '0.69897']

>>> df.select(log(df.age).alias('e')).map(lambda l: str(l.e)[:7]).collect()
['0.69314', '1.60943']
"""
sc = SparkContext._active_spark_context
jc = sc._jvm.functions.log(base, _to_java_column(col))
if arg2 is None:
jc = sc._jvm.functions.log(_to_java_column(arg1))
else:
jc = sc._jvm.functions.log(arg1, _to_java_column(arg2))
return Column(jc)


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4 changes: 4 additions & 0 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/math.scala
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Expand Up @@ -258,6 +258,10 @@ 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") {

/**
* Natural log, i.e. using e as the base.
*/
def this(child: Expression) = {
this(EulerNumber(), child)
}
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@yjshen yjshen Jun 19, 2015

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I prefer to remove this single parameter constructor, because this would make both ln and log(c) express the same thing in a SQL expression.

And also complex the binary log here to check its first argument branch in both eval & genCode

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@rxin rxin Jun 19, 2015

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I think that's a good idea. Can you fix it in your pr? I'm gonig to merge this one first.

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@yjshen yjshen Jun 19, 2015

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Yes, already fix this in my pr. :)

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