Python filter() 函數是另一個[內置]函數,Helpful when working with data.filter() Except that the function accepts a sequence as input,Actually also accepts a function as input,and returns an iterator constructed from the items in the given sequence,對於這些項目,The given function returns true.If you want to collect everything in the result at the same time,你可以對filterThe resulting iterator call[list()]函數.
We recently learned[Python 中的 lambda 函數],They are discussed with us herefilter()It is very common to use functions together.讓我們看一個實際的例子,Look at a list of numbers,Only even numbers are filtered out.
# Python Program to find even numbers
# from a list using an anonymous function
# Take a list of numbers.
list_of_ints = [1, 2, 3, 4, 5, 6, 7, 8, 9]
# use anonymous lambda function to filter
result = list(filter(lambda x: (x % 2 == 0), list_of_ints))
# printing the result
print(result)
復制代碼[2, 4, 6, 8]
復制代碼The next example is to look at a list of strings.Some of these strings are palindromes.This means their reverse spelling is the same as normal.我們可以使用filter()和lambda函數,Only palindromes in the list are found.
# Python Program to find palindromes in a list of strings.
list_of_strings = ['ferrari', 'racecar', 'tesla', 'level', 'technoking']
# use an anonymous function to filter palindromes.
result = list(filter(lambda x: (x == ''.join(reversed(x))), list_of_strings))
# print the palindromes
print(result)
復制代碼['racecar', 'level']
復制代碼我們也可以使用 Python 中的標准defkeyword to define a named function,Then combine this named function with filter() 函數結合使用.Here we will create a function that can filter odd numbers from a list.
# list of numbers
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
# function that finds odd numbers
def is_odd(num):
if (num % 2) != 0:
return True
else:
return False
results = filter(is_odd, numbers)
print(list(results))
復制代碼[1, 3, 5, 7, 9, 11]
復制代碼meats1 = ['steak', 'chicken', 'pork', 'bacon', 'ground beef']
meats2 = ['sausage', 'pork', 'duck', 'lamb', 'steak']
# function that filters duplicate string
def filterDuplicate(string_to_check):
if string_to_check in the_list:
return False
else:
return True
# Using filter() to remove duplicate strings
the_list = meats2
results = list(filter(filterDuplicate, meats1))
the_list = meats1
results += list(filter(filterDuplicate, meats2))
print("Duplicates removed: ", results)
復制代碼Duplicates removed: ['chicken', 'bacon', 'ground beef', 'sausage', 'duck', 'lamb']
復制代碼要理解 filter() A key concept of functions is ,It's checking for one True 條件.Only true values pass the filter.我們可以通過將Python的NoneThe value is passed to as a functionfilter()來證明這一點,The function will still work.Let's look at the concept here.
# list of values
list_of_values = ['1', 2, 0, False, True, '1', [], {}]
filtered_list = filter(None, list_of_values)
print('The filtered elements are:')
for element in filtered_list:
print(element)
復制代碼The filtered elements are:
1
2
True
1
復制代碼到目前為止,We've seen how some are used in various lists filter() 的例子.我們還可以在 Python used for dictionaries filter() 函數.
dictOfNames = {
0: 'Rick',
1: 'Vick',
2: 'Bob',
3: 'Rob',
4: 'Soham',
5: 'Dave'
}
# Filter dictionary by keeping elements whose values contain
# the letter 'a'
newDict = dict(filter(lambda elem: 'a' in elem[1], dictOfNames.items()))
print('Filtered Dictionary : ')
print(newDict)
復制代碼Filtered Dictionary :
{4: 'Soham', 5: 'Dave'}
復制代碼filter() The function constructs an iterator from the elements of an iterator,for this iterator,一個函數返回 true.其工作方式是 filter() Method filters the given iterator with the help of a function,This function tests whether each element in the iterator is true.
filter()函數的語法如下：
filter(function, iterable)
filter()的參數是function和iterable.
filter()函數返回一個迭代器,The iterator passes the function check for each element in the iterator.
使用lambda時,filter()函數的語法如下：
filter(lambda item: item[] expression, iterable)
