Map is a built-in Python function. It takes a function and an iterable for an argument:
map(aFunction, iterable)
The function is applied on all the elements of the iterable and results are returned as a list. As a function is passed to map, lambda is most commonly used along with map.
Let's see an example on how to use a map function:
#First let us declare a list. a =[10,20,30] # Let us now call the map function in our Print statement. print map(lambda x:x**2,a)
This is very similar to the code in the previous recipe. A map functions takes two parameters. The first one is a function and second one is a sequence. In our example code, we used an anonymous function:
lambda x:x**2
This function squares the given input. We also passed a list to map.
Map applies a function that squares all the elements in the given list and returns the result as a list.
The output is as follows:
[100,400,900]
Similarly, any other function can be applied to a list:
print map(lambda x:x**3,a)
Using map, we can replace the code snippet in the previous recipe with a single line:
print sum(map(lambda x:x**2,a)) print sum(map(lambda x:x**3,a))
Map expects an N-argument function if we have N-sequences. Let's see an example to understand this:
a =[10,20,30] b = [1,2,3] print map(pow,a,b)
We passed two sequences a and b to our map function. Notice that the function passed is the power function. It takes two arguments. Let's see the result of the preceding code snippet:
[10, 400, 27000] >>>
As you can see, the elements of list a is raised to the power of value in the same position in list b. A point to note is that both the lists should be of the same size; if not, Python will fill the smaller list with None. Though our examples are operating on a list, any iterable can be passed to a map function.