Introduction to Python built-in functions in filtermapreduce

Python has built-in interesting and useful functions, such as filter, map, and reduce, which are used to process a set. filter is easy to understand for filtering and map for ING, reduce is used for merging. it is a trigger of the Python list method. Python has some very interesting and useful functions, such as filter, map, and reduce, which are used to process a set, filters are easy to understand for filtering, map for ing, and reduce for merging. it is the trigger of the Python list method.

1. filter functionThe function is equivalent to a filter. Call a Boolean function bool_func to iterate over the elements in each seq. return a sequence of elements that make bool_seq return true.

>>> N=range(10)>>> print filter(lambda x:x>5,N)[6, 7, 8, 9]

2. map functionsFunc acts on each element of a given sequence and uses a list to provide the return value.

>>> N1=[1,2,3]>>> N2=[6,5,4]>>> map(lambda x,y:x+y,N1,N2)[7, 7, 7]>>> map(lambda x:x+3,N1)[4, 5, 6]

3. reduce function, Func is a binary function that acts on the elements of the seq sequence, each carrying a pair (previous results and the elements of the next sequence ), continuously apply the existing results and the next value to the subsequent results, and finally reduce our sequence into a single return value.

>>> N=range(1,101)>>> reduce(lambda x,y:x+y,N)5050

Example 1: Use map and reduce to add 5 factorial (5! + 4! + 3! + 2! + 1 !)

>>>print reduce(lambda x,y:x*y,range(1,6))>>>print reduce(lambda x,y:x*y,range(1,5))>>>print reduce(lambda x,y:x*y,range(1,4))>>>print reduce(lambda x,y:x*y,range(1,3))>>>print reduce(lambda x,y:x*y,range(1,2))'''

Result:

12024621'''

# Convert the result from the previous step into a factorial list

>>>print map(lambda a:reduce(lambda x,y:x*y,range(1,a+1)),range(1,6))[1, 2, 6, 24, 120]

# Add the factorial list. The first question is solved.

>>>print reduce(lambda m,n:m+n,map(lambda a:reduce(lambda x,y:x*y,range(1,a+1)),range(1,6)))153

Example 2: Use filter to convert 100 ~ Filter out prime numbers of less than 200
Prime number. In a natural number greater than 1, except for 1 and the integer itself, it cannot be divisible by other natural numbers.

>>>filter(lambda N:len(filter(lambda M:N%M==0,range(2,int(N**0.5)+1)))==0,range(100,201))