## 2018年6月8日 星期五

### [ Python 常見問題 ] How to find all occurrences of an element in a list?

Source From Here
Question
index() will just give the first occurrence of an item in a list. Is there a neat trick which returns all indices in a list?

How-To
You can use a list comprehension:
>>> alist = [1, 2, 3, 3, 2, 4, 1, 5, 6, 5, 5, 7]
>>> indices_of_2 = [i for i, v in enumerate(alist) if v == 2] # Collecting index of value=2
>>> indices_of_2
[1, 4]

A functional programming way for reference:
1. def foldLeft(alist, identity, fun):
2.     rst = identity
3.     for e in alist:
4.         rst = fun(rst, e)
5.     return rst
6.
7. def indexAll(rst, t, n):
8.     def ia(rst, t):
9.         if t[1] == n:
10.             rst.append(t[0])
11.         return rst
12.     return ia
13.
14. foldLeft(list(enumerate(alist)), [], indexAll(2))  # Return index of '2' = [1, 4]
15. foldLeft(list(enumerate(alist)), [], indexAll(5))  # Return index of '5' = [7, 9, 10]

### [ JS 常見問題 ] Time difference in Nodejs?

Source From   Here   Question   Im trying to figure out a way to   get the time difference in seconds between two dates . For example, diff...