Adding 0's to cell array such that each column contains an equal number of entries - MATLAB

Question

I have a 16x100 (varies in size) cell array and I would like to extract each of it's columns into a column of a matrix. When each column of the cell array contains an identical number of entries I can use:

elem = numel([dist{:,1}]);
repeat = size(dist,2);
data = zeros(elem,repeat);  
for k=1:repeat
  results(:,k) = [dist{:,k}]';
end

However there are some instances where there are not an equal number thus it returns the error:

Subscripted assignment dimension mismatch.

What is the best way around this? Is there a way to add zeroes to equalise the number of entries?

What does the cell array contain? Post a minimal example dist and desired output — Luis Mendo
– Luis Mendo, Commented Feb 26, 2015 at 10:47

Community · Accepted Answer · 2017-05-23 11:56:55Z

1

Perfect setup for bsxfun's masking capability here!

Now, I am assuming your data is setup as described in your previous question -

enter image description here

To solve the case of filling up "empty spaces" with zeros, you can setup an output array with maximum possible number of elements in each column and then fillup the valid spaces with the values from the input cell array, with the valid spaces being detected by the logical mask created with bsxfun. Read on through the comments inlined within the code listed next to find out the exact ideas on solving it -

%// Get the number of elements in each column of the input cell array
lens = sum(cellfun('length',a),1)

%// Store the maximum number of elements possible in any column of output array
max_lens = max(lens)  

%// Setup output array, with no. of rows as max number of elements in each column
%// and no. of columns would be same as the no. of columns in input cell array 
results = zeros(max_lens,numel(lens))

%// Create as mask that has ones to the "extent" of number of elements in
%// each column of the input cell array using the lengths
mask = bsxfun(@le,[1:max_lens]',lens)  %//'

%// Finally, store the values from input cell array into masked positions
results(mask) = [a{:}]

edited May 23, 2017 at 11:56

CommunityBot

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answered Feb 26, 2015 at 12:17

Divakar

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2 Comments

AnnaSchumann Over a year ago

Wow! I've been looking for an excuse to learn how to use bsxfun for a while now. Thanks!

Divakar Over a year ago

@AnnaSchumann Hey! you must!:) It's THE best tool out there to do almost anything on MATLAB!

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