How to rightly locate a value at an index in nd array and save it as list in python?

问题

I have a list called L. It has C number of elements.

I have a nd array called X. X has Boolean data (either 0 or 1). It has dimension as (20,C). There are 20 lists with each list having C number of elements

I want to locate each index that has value of 1 in X.Then I want the value at this same index in List L, and finally store this value from L in another nd array . I write the following code

emptylist=[]

for index,value in np.ndenumerate(X): #this index is a tuple like (0,3)

tuple_to_list=list(i)
if value == 1:

   emptylist.append (L[tuple_to_list[1]])  #error 

the program does not stop running. Can you guide me to improve this code ?

回答1:

the last line should be:

empylist.append(L[index[0]])

and I don't see what your tuple_to_list is needed for

A solution using only arrays would be the following:

L = list(np.random.rand(20)) # gives a List of radom values (to be compatible to the question)
La = np.array(L)
X = randint(0,5,(20,101)) # make an array having values from 0...4
emptylist = La[np.where(X==1)[0]] #gives those rows of L where rows of X contain 1

though the name empty is not appropriate anymore.

来源：https://stackoverflow.com/questions/40345872/how-to-rightly-locate-a-value-at-an-index-in-nd-array-and-save-it-as-list-in-pyt