Simple way of accessing arrays in cell arrays

Question

I'm looking for a quick, simple way of accessing specific arrays that are inside cell arrays. For example, let's say I have

A = rand(10,2);
B = rand(15,1);
C = rand(130,1);
D = rand(16,1);
E = rand(1000,25);
my_cell = {A,B,C,D,E};

Let's say I want the 1st, 2nd, and 4th matrices only (i.e., A, B and D) inside a new cell array. So the new cell array would be composed of {A, B, D}. This is obviously easy using a for loop:

idx=[1,2,4];
new_cell=cell(1,length(idx));
for i=1:length(idx)
   new_cell{i}=my_cell{idx(i)};
end

I was wondering if there was an even quicker/simpler way. Maybe there's an obivous indexing trick or function I'm not aware of? I'd appreciate the help.

Tasos Papastylianou · Accepted Answer · 2016-09-10 23:41:11Z

3

Yes, you can index your cell array like a normal array (i.e. using parentheses instead of brackets). Actually, it is a "normal" array: it's a normal array of "cell" elements. So indexing them like a normal array simply returns the individual "cell elements" rather than their contents.

Therefore you can just do

my_cell(idx)

EDIT: Just to make the difference clear between "indexing a cell like an array" and "collecting the comma-separated-output into a new cell array" approaches:

>> my_cell = {'A','B','C'; 'D','E','F'; 'G', 'H', 'I'}    
my_cell = 
    'A'    'B'    'C'
    'D'    'E'    'F'
    'G'    'H'    'I'

>> my_cell(1:2,1:2)
ans = 
    'A'    'B'
    'D'    'E'

>> {my_cell{1:2,1:2}}  % this will ALWAYS be a horizontal cell vector
ans = 
    'A'    'D'    'B'    'E'

edited Sep 10, 2016 at 23:41

answered Sep 10, 2016 at 23:23

Tasos Papastylianou

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1 Comment

John Alberto Over a year ago

Doesnt get simpler than this :) Thanks

Mingjing Zhang · Accepted Answer · 2016-09-10 23:28:44Z

1

{my_cell{idx}} should do the trick.

my_cell{idx} returns the elements in my_cell indexed by idx as a comma separated list. It is equivalent to A, B, D. All you need to do is to close this list with {} to make a cell array out of it.

answered Sep 10, 2016 at 23:28

Mingjing Zhang

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2 Comments

Tasos Papastylianou Over a year ago

note. this approach will not work if you wish to preserve structure. Change your original cell to my_cell = {A;B;C;D;E} and you'll see what I mean.

John Alberto Over a year ago

Awesome! Thanks for the heads up about the structure. I see what you mean.

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