Advanced python concepts the easy way ( Lambda , Map and Filter )
This is continuation to previous article on Using advanced Python concepts the easy way.
In this article I'll cover up:
- Lambda
- Map
- and Filter
Lambda
Lambda is simply a one-liner function. It can take some arguments and can have one experssion in it to execute. This comes very handy with map and other functions, where we need to execute a one liner experssions in for every element of list.
Syntax begins with a lambda keyword and arguments then expression.
lambda arguments : expression
Here is a simple lambda to calculate square of any number.
>>> Get_Sqr = lambda x: x * x
>>> Get_Sqr(9)
81
This is equivalent to a function declared normal way, like this:
def GetSquare(x):
return x*x
GetSquare(9)
81
Map
Map is used to iterate over a list / sequence and apply lambda / function to every element. You can do the same with list comprehensions also.
map(function or lambda , sequence or list)
Let's use our previous lambda to print square of every number of a list.
Map will return an iteratanle object, so we need to wrap it a with they type we need. Here we will wrap it with list.
arr = [1, 2, 3, 4, 5]
arr = list(map(lambda x : x*x, arr))
print (arr)
[1, 4, 9, 16, 25]
Filter
Filter will apply a lambda / function to all the elements of the given sequence and will return an iteratable object of all the elements for which lambda / function returned true.
filter(function or lambda, sequence or list)
Let's use filters to get all the odd numbers of a list.
arr = [1, 2, 3, 4, 5, 6]
arr = list(filter(lambda x : x%2 != 0, arr))
print (arr)
[1, 3, 5]
In upcoming article I'll talk about Iteration protocol and generators.
