Matlab：如何使用特定索引的字符串构建数组

Question

I have a cell array of strings (length = 4):
A = {'a', 'b', 'c', 'd'}
I have a double matrix of indices (length = 4):
B = [2, 4, 6, 8]

How can I create a new cell array C (of strings) of length = 8 , that uses the indices in B to place the strings from A into the new array C . For any index not specified in B , I want to enter a ' ' space (empty string). Note: my real data does not go "every-other".

C = {' ', 'a', ' ', 'b', ' ', 'c', ' ', 'd'}

How can this be done in Matlab?

Answer 1

This is another approach, very similar to the above, but no repmat .

C(B)=A;
C(cellfun('isempty',C))={' '}; 

I have replaced traditional @isempty since it may be faster . Thanks @LuisMendo for mentioning that in a comment.

Answer 2

One possible approach:

C = repmat({' '}, 1, max(B)); %// predefine with ' ';
C(B) = A; %// replace actual values

Or:

C(B) = A; %// this automatically fills missing values with [] 
ind = cellfun('isempty', C); %// find occurrences of [] 
C(ind) = repmat({' '}, 1, sum(ind)); %// replace them with ' '

The last line could be simplified as follows (no repmat needed), as noted by @ParagS.Chandakkar:

C(ind) = {' '}; %// replace them with ' '