Search through Cell

Hi, I have problem working with cells.

I have a 1 x 4 cell with each cell containing an N X 1 column vector. How do I search through all the first three cell elements for the rows having a given value.

To illustrate further, if I a matrix, A = N X 4; and want to find where the values 0 occur, I do

 [row column] = find(A(:,1:3) == 0);

So, essentially what I am looking for is its equivalent command for a cell.

Answer 1

[Jan]

What about a trivial FOR loop:

C      = {rand(100, 1), rand(100, 1), rand(100, 1), rand(100, 1)};
value  = 0.5;
row    = cell(1, 3);
column = cell(1, 3);
for i = 1:3
  [row{i}, column{i}] = find(C{1} == value);
end

This can be done by CELLFUN also, but I do not see an advantage.

Or you can create the numerical matrix explicitely and use logical indexing:

Match = find(cat(2, C{1:3}) == value);

Usually using the columns of the logical matrix Match is faster than using separate index vectors.

[Charles]

Hi, thanks for your response. A loop would be too expensive as there I have more than 20 million rows. What I did initially was to create a matrix from the cell and then search using the method that I described before, but I did not want to create extra variables. Anyway, I think your last suggestion will do it.

Answer 2

[Daniel Shub]

A = cell2mat(A);
[row column] = find(A(:,1:3) == 0);
A = mat2cell(x, N, [1, 1, 1, 1]);