The reduce () function of 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:

First two elements are computed: F (1, 3), the result is 4, the result and the 3rd element is calculated: F (4, 5), the result is 9, and the result and the 4th element is calculated: F (9, 7), the result is 16, and then the result and the 5th element calculation: F (16, 9), the result is 25; End of calculation, return result 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.

The reduce () function of Python