过滤序列元素
一、 解决问题
有一个数据序列，想利用一些规则从中提取出需要的值或者是缩短序列
二、解决方案
列表推导
生成器表达式
filter()
itertools.compress()
三、代码说明
mylist = [1, 4, -5, 10, -7, 2, 3, -1]
newList = [i for i in mylist if i > 0]
print(type(newList)) # -><class 'list'>
print(newList) #->[1, 4, 10, 2, 3]
#列表推导可以操作
newList = [i + 1 for i in mylist if i > 0]
print(newList) #->[2, 5, 11, 3, 4]
#过滤变种，将不符合的值变掉，而不是删除它们
newList = [n if n > 0 else 0 for n in mylist]
print(newList) #->[1, 4, 0, 10, 0, 2, 3, 0]#生成器表达式
newList = (i for i in mylist if i > 0)
print (type(newList)) # -> <class 'generator'>#内建函数filter()
values = ['1', '2', '-3', '-', '4', 'N/A', '5']
def is_int(val):
try:
x = int(val)
return True
except ValueError:
return False
#filter 返回一个迭代器
isVals = list(filter(is_int, values))
print(isVals) #->['1', '2', '-3', '4', '5']# itertools.compress()
addresses = [
'5412 N CLARK',
'5148 N CLARK',
'5800 E 58TH',
'2122 N CLARK'
'5645 N RAVENSWOOD',
'1060 W ADDISON',
'4801 N BROADWAY',
'1039 W GRANVILLE'
]
counts = [0, 3, 10, 4, 1, 7, 6, 1]
from itertools import compress
more5 = [n > 5 for n in counts]
print(more5) #[False, False, True, False, False, True, True, False]
newList = list(compress(addresses, more5))
print(newList) #['5800 E 58TH', '4801 N BROADWAY', '1039 W GRANVILLE']四、关联知识
五、总结
六、代码地址
github地址:https://github.com/weichen666/python_cookbook
目录/文件：first_selection/learn_list_reduce.py