Lambda_Expressions_basics.md

Lambda Functions basics

Lambda functions = Anonymous functions

A lambda function is a small function containing a single expression. Lambda functions can also act as anonymous functions where they don’t require any name. These are very helpful when we have to perform small tasks with less code.

Python Example

Python programming language supports the creation of anonymous functions (i.e. functions defined without a name), using a construct called lambda.

The general structure of a lambda function is:

lambda <arguments>: <expression>

Here is a simple python function to double the value of a scalar:

 def f(x): 
   return x*2
 #end-def

For instance to use this function:

 print(f(4))
 8

The same function can be written as lambda function:

>>> g = lambda x: x*2
>>> g
<function <lambda> at 0x105668b90>
>>> g(10)
20

PySpark Example

You may use lambda expressions or functions in PySpark:

PySpark Example using lambda

# rdd: RDD[(String, Integer)]
# x : (String, Integer)
rdd2 = rdd.filter(lambda x: x[1] > 0)

PySpark Example using function

# x : (String, Integer)
def filter_function(x):
	if (x[1] > 0):
		return True
	else:
		return False
#end-def

# rdd: RDD[(String, Integer)]
rdd2 = rdd.filter(filter_function)