Use of the reduce function in Python

The reduce () function is also a high-order function built into Python.

The reduce () function receives a parameter similar to map (), a function f, a list, but behaves differently from map (), and reduce () the incoming function f must receive two parameters, and reduce () calls function f repeatedly on each element of the list, and returns the final result value.

For example, write an F function that receives x and Y, and returns the and of X and Y:

def f(x, y):      return x  + y

When you call reduce (f, [1, 3, 5, 7, 9]) , the Reduce function calculates the following:

先计算头两个元素：f( 1 ,  3 )，结果为 4 ； 再把结果和第 3 个元素计算：f( 4 ,  5 )，结果为 9 ； 再把结果和第 4 个元素计算：f( 9 ,  7 )，结果为 16 ； 再把结果和第 5 个元素计算：f( 16 ,  9 )，结果为 25 ； 由于没有更多的元素了，计算结束，返回结果 25

The above calculation is actually a summation of all the elements of the list. Although Python has built-in sum function sum (), it is simple to sum with reduce ().

reduce () can also receive a 3rd optional parameter as the initial value of the calculation. If you set the initial value to 100, the calculation:

reduce (f, [ 1 ,  3 ,  5 ,  7 ,  9 ],  100 )

The result will change to 125 because the first round calculation is:

Computes the initial value and the first element:F (1), the result is 101.

After Python 3.0.0.0, reduce is no longer in the built-in function, and it has to be from functools import reduce.

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Use of the reduce function in Python