Python cookbook(数据结构与算法)筛选及提取序列中元素的方法

# Examples of different ways to filter data
mylist = [1, 4, -5, 10, -7, 2, 3, -1]
print('mylist=',mylist)
# 使用列表推导式
pos = [n for n in mylist if n > 0]
print('正数为：',pos)
neg = [n for n in mylist if n < 0]
print('负数为：',neg)

mylist= [1, 4, -5, 10, -7, 2, 3, -1]
正数为： [1, 4, 10, 2, 3]
负数为： [-5, -7, -1]

mylist = [1, 4, -5, 10, -7, 2, 3, -1]
print('mylist=',mylist)
# 使用生成器表达式
pos = (n for n in mylist if n > 0)
print('生成器为',pos)
for x in pos:
 print(x)

mylist= [1, 4, -5, 10, -7, 2, 3, -1]
生成器为 <generator object <genexpr> at 0x02421FD0>
1
4
10
2
3

values=['1','2','-3','-','N/A','4','5','%']
def is_int(val): #将处理筛选逻辑的代码放到单独的函数
 try:
  x=int(val)
  return True
 except ValueError:
  return False
ivals=list(filter(is_int,values)) #使用filter(func,list)进行过滤
print(ivals)

['1', '2', '-3', '4', '5']

# Negative values clipped to 0
neg_clip = [n if n > 0 else 0 for n in mylist]
print('负数替换为0，结果：',neg_clip)
# Positive values clipped to 0
pos_clip = [n if n < 0 else 0 for n in mylist]
print('正数替换为0，结果：',pos_clip)
'''

mylist= [1, 4, -5, 10, -7, 2, 3, -1]
负数替换为0，结果： [1, 4, 0, 10, 0, 2, 3, 0]
正数替换为0，结果： [0, 0, -5, 0, -7, 0, 0, -1]

# 采用筛选工具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 ]
a = list(compress(addresses, more5))
print(a)

['5800 E 58TH', '1060 W ADDISON', '4801 N BROADWAY']