Find in a cell array?

Hello all,

Suppose a cell array 10x1 consisted of random numbers from 1 to 5. How can I find the locations for number 5?

All the best,

MhD

[Jan]

I've deleted the duplicate question.

[Elias Berra]

X = my_array_data [row,col] = find(X==21) %In this example, it retrieves the cell location which contains the value 21.

[Marwan Malaeb]

call this array for example X

type k=find(X==5)

it will return for you the number of the cell that has the value of 5.

Answer 1

[Jan]

C = {1,5,3,4,2,3,4,5,2,1};
index = find([C{:}] == 5);

Here [C{:}] is a faster inlined version of cell2mat.

Alternative:

index = cellfun(@(x) x==5, C, 'UniformOutput', 1);

Or the long and most likely faster form:

index = false(1, numel(C))
for k = 1:numel(C)
  index(k) = (C{k} == 5);
end

[EDITED] If you are talking of a cell string, this is much faster:

D = {'1' '5' '3' '4' '2' '3' '4' '5' '2' '1'};
index = find(strcmp(D, '5'));

[M G]

Hey Jan,

Nice help. I just do not understand the difference between following two: C=[1] [5] [3] [4] [2] [3] [4] [5] [2] [1] ... which is what you said in your example and:

D='1' '5' '3' '4' '2' '3' '4' '5' '2' '1'

which I have the problem with. Both of them are cell arrays.However, your suggested way unfortunately doesn't work with "D".

Any idea to help me understand is appreciated :)

All the best....

[Jan]

Please do not write only "does not work", but explain what happens instead: Do you get an error message or does the result differ from your expectations?

It would be useful, if you post the real data directly to the question, because then the other users do not waste your and their time with not matching suggestions. Not that "D='1' '5'..." is not valid Matlab syntax, because the surrounding braces are essential.

While I expect my code to work with D fluently, when you search for the character '5' instead of the number 5. But Matlab offers a much faster solution then, see [EDITED]

[M G]

strcmp works! Thanks. Here is data:

https://dl.dropboxusercontent.com/u/19202474/eheader.zip

Here is how it worked based on what you suggested.

S = char(cellfun(@(x) num2str(x),eheader,'Un',0))
Index = [];
j=1;
for i=1:size(S,1)
    if(strcmp(S(i,:),'    -88  ')==1)
       Index(j) = i;
       j = j+1;
    end
end

[Jan]

This looks strange. When eheader is numerical, converting it elementwise inside a cellfun call to a string and afterwards by char to a char matrix is cruel. Then assuming a certain number of spaces around the value is fragile, because the width depends on the values. What about this (I cannot open the posted MAT file, better post code in the forum which creates the example data):

x = find([eheader{:}] == -88)

STRCMP works much faster with cell strings, so at least do not let CHAR() create a CHAR-matrix.

[Kylie Hansen]

Just a casual MATLAB coder dropping by this older thread on a hunt for answers. Your response for the cell string method worked easily for me. Thank you so much for including it!

Answer 2

[Bill Tubbs]

Just in case someone comes here looking to do this with a cell array of chars as I was, it's quite easy this way:

my_cell_array = {'a', 'b', 'c'};
i = find(strcmp(my_cell_array, 'b'));
assert(i == 2)

[hongyi xu]

Genius! Your supplement exactly fits my question.

Answer 3

[Caroline]

cellarray_new = zeros; %initializing the array 
ind = 1; %indices for new array
for j = 1:10
  if (cellarray(j) == 5)
      cellarray_new(ind) = j;
      ind = ind + 1;
  end
end

the array cellarray_new will contain all the indices of the original cell array that contain the number 5

[Azzi Abdelmalek]

Why initializing cellarray_new to 0?

[Jan]

I assume that "cell array" implies, that the array is a cell.

[Filza Ashraf]

how can i find a pixel intensity if cell contains an image or image is stored in cell???