在Python中使用 map()函数求和二维数组

给定一个二维矩阵，我们需要找到矩阵中所有元素的总和？

例子：

Input  : arr = [[1, 2, 3], 
                [4, 5, 6], 
                [2, 1, 2]]
Output : Sum = 26

这个问题可以通过迭代整个矩阵使用两个 for 循环轻松解决，但我们可以在Python中使用 map()函数快速解决这个问题。

# Function to calculate sum of all elements in matrix
# sum(arr) is a python inbuilt function which calculates
# sum of each element in a iterable ( array, list etc ).
# map(sum,arr) applies a given function to each item of 
# an iterable and returns a list of the results.
def findSum(arr):
  
    # inner map function applies inbuilt function  
    # sum on each row of matrix arr and returns 
    # list of sum of elements of each row
    return sum(map(sum,arr))  
  
# Driver function
if __name__ == "__main__":
    arr = [[1, 2, 3], [4, 5, 6], [2, 1, 2]]
    print ("Sum = ",findSum(arr))

输出：

26

map() 有什么作用？
map()函数将给定函数应用于可迭代（列表、元组等）的每个项目并返回结果列表。例如，请参见下面给出的示例：

# Python code to demonstrate working of map()
  
# Function to calculate square of any number
def calculateSquare(n):
    return n*n
  
# numbers is a list of elements
numbers = [1, 2, 3, 4]
  
# Here map function is mapping calculateSquare 
# function to each element of numbers list.
# It is similar to pass each element of numbers 
# list one by one into calculateSquare function 
# and store result in another list
result = map(calculateSquare, numbers)
  
# resultant output will be [1,4,9,16]
print (result)

输出 ：

[1, 4, 9, 16]