python - python中是否有与R的“which”函数相当的函数？

Question

R 'which' 函数是一种在长字符向量字符串中查找字符的有效且并行化的方法。有没有在python中实现这个功能或简单的方法？

Answer 1

如果这些元素满足特定条件，则获取可枚举集合中元素索引的pythonic方法是将列表推导与enumerate()一起使用。例如，要查找列表中奇数元素的所有索引：

>>> mylist = [1,2,3,4,5,6,7,8]
>>> [index for index, item in enumerate(mylist) if item%2]
[0, 2, 4, 6]

Answer 2

我不太确定 R 是如何工作的，但这里有一些想法可以帮助您入门

lookingFor = 'a'
print "the string of all '%s's is" %lookingFor, ''.join(char for char in myLongString if char==lookingFor)
print "there are %s many instances of the character '%s' in the string '%s'" %(myLongString.count(lookingFor), lookingFor, myLongString)
import collections
print "there are %s many instances of the character '%s' in the string '%s'" %(collections.Counter(myLongString)[lookingFor], lookingFor, myLongString)

Answer 3

或包装成通用函数：

>>> which = lambda targetList, f: [index for index, item in enumerate(targetList) if f(item)]

例如：

>>> mylist = [1,2,3,4,5,6,7,8]
>>> which(mylist, lambda x: x % 2)