How to create cell-array in MATLAB and initialize all elements to the same object?

Question

I have a matrix (call it X) that is initialized to say zero(3).

I want to change the code so that X is a cell array of size (say) (3,1) and initialize each element to zero(3).

I can do it with a loop but is there a better way?

X = cell(3,1);
for ii=1:numel(X)
    X{ii} = zeros(3);
end

score 10 · Answer 1 · answered Sep 19 '13 at 10:06

10

An alternative way:

X = repmat({zeros(3)}, 3, 1);

another one:

X = cell(3,1);
X(:) = {zeros(3)};

answered Sep 19 '13 at 10:06

Amro

The alternatives have the advantage that the size of X is determined on the same line as the new content. I would prefer them to deal. deal probably is best used in some other connection. – NoDataDumpNoContribution Jan 31 '14 at 08:19
Fantastic trick! Thanks – Massimo Aug 28 '23 at 00:25

score 10 · Accepted Answer · answered Nov 19 '11 at 17:43

10

You can do this with deal().

>> [X{1:3, 1}] = deal(zeros(3))

X = 

    [3x3 double]
    [3x3 double]
    [3x3 double]

answered Nov 19 '11 at 17:43

John Colby

Note that this is not safe if `X` already exists. For example if it was defined like this before `[X{1:4, 1}] = deal(zeros(4))` – Dennis Jaheruddin Sep 19 '13 at 10:29

score 3 · Answer 3 · answered Sep 19 '13 at 10:22

3

And yet another way:

X = {zeros(3)};
X(1:3,1) = X;

This solution uses the fact that you can assign to indices that lie beyond the variables size. Matlab will automatically expand in this case.

Similarly:

clear X;
X(1:3,1) = {zeros(3)};

answered Sep 19 '13 at 10:22

Dennis Jaheruddin

3 Answers3