有没有python方法根据提供的新索引重新排序列表？

Question

Say I have a working list: ['a','b','c'] and an index list [2,1,0] which will change the working list to: ['c','b','a']

Is there any python method to do this easily (the working list may also be a numpy array, and so a more adaptable method is greatly preferred)? Thanks!

Answer 1

• ordinary sequence:

   L = [L[i] for i in ndx] 

• numpy.array :

   L = L[ndx] 

Example:

>>> L = "abc"
>>> [L[i] for i in [2,1,0]]
['c', 'b', 'a']

Answer 2

Converting my comment-answer from when this question was closed:

As you mentioned numpy, here is an answer for that case:

For numerical data , you can do this directly with numpy arrays Details here: http://www.scipy.org/Cookbook/Indexing#head-a8f6b64c733ea004fd95b47191c1ca54e9a579b5

the syntax is then

myarray[myindexlist]

For non-numerical data , the most efficient way in the case of long arrays which you read out only once is most likely this:

(myarray[i] for i in myindex) 

note the () for generator expressions instead of [] for list comprehension.

Read this: Generator Expressions vs. List Comprehension

Answer 3

This is very easy to do with numpy if you don't mind converting to numpy arrays:

>>> import numpy
>>> vals = numpy.array(['a','b','c'])
>>> idx = numpy.array([2,1,0])
>>> vals[idx]
array(['c', 'b', 'a'], 
      dtype='|S1')

To get back to a list, you can do:

>>> vals[idx].tolist()
['c', 'b', 'a']