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Find index of cells containing my string

Asked by New
on 25 Feb 2011
Latest activity Commented on by Omer Moussaffi on 19 Apr 2017

Hi, I have a cell aray (40,000X1)in which every cell contains a string. I would like to find the indexes of the cells containing a specific string.

I used the following:

Index = strfind(Mycellarray, 'Bla');

I get the following error: ??? Error using ==> cell.strfind at 35 If any of the input arguments are cell arrays, the first must be a cell array of strings and the second must be a character array.

What is wrong, in the help file strfind accepts cell arrays and a pattern...?

Thank you

  5 Comments

Hi
Thank you for your answers. I used C2 = [C{:}] as advised but then still trying to get the list of Indices I used:
Index = strfind(C2,'bla')
I get a cell array in which every cell is either empty [] or 1 but no list of indices.
K.

I found out that if the cell has empty indexes it wont work. Example:

a =

    'hey'
    'oh'
       []

>> strfind(a,'hey')

??? Error using ==> cell.strfind at 35 If any of the input arguments are cell arrays, the first must be a cell array of strings and the second must be a character array.

>> a{3} = 'letsGo'

a =

    'hey'
    'oh'
    'letsGo'

>> strfind(a,'hey')

ans =

    [1]
    []
    []

It is not considered as a cell string if all the cells in the array have a string in them.

@Felipe: Exactly. A cell is a cell string, if it contains strings only. And STRFIND works on strings and cell strings only.

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8 Answers

Answer by Jan Simon
on 25 Feb 2011
Edited by Jan Simon
on 7 Mar 2017
 Accepted Answer

Do you want to search for the string 'bla' inside each string of the cell array, or should the cell element be 'bla' exactly? The answering would be easier, if you explain this detail.

If 'bla' should be part of the string:

IndexC = strfind(C, 'bla');
Index = find(not(cellfun('isempty', IndexC)));

If the string should be excatly 'bla': See Jos' answer.

 

[EDITED] Alexander Cranney explained, that MATLAB 2016b has a command for this:

Index = find(contains(C,'bla'));

  3 Comments

Possibly bla might occur multiple times and the indices of all of the positions is what is desired?

A little correction to Jan's answer:

   IndexC = strfind(C, 'bla'); % not C2
   ...

No need to convert C into string from cell : C2 = [C{:}];

As of MATLAB 2016b, there is a new function "contains" that does exactly this!

    % code
Index = find(contains(C,'bla'));

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Answer by Matt B
on 14 Nov 2013

I realize this question is old now, but a simple way of doing this is to define an inline function:

cellfind = @(string)(@(cell_contents)(strcmp(string,cell_contents)));

You can then use this with cellfun to return a boolean value for each element of the cell. For example:

cell_array={1,eye(2),true,'foo',10};
string='foo'
logical_cells = cellfun(cellfind('foo'),cell_array)
logical_cells = 
                 [0,0,0,1,0]

  2 Comments

Great answer. Works very well.

The inline function was a life saver!

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Answer by Jay
on 28 May 2016
Edited by Jay
on 28 May 2016

This worked for me:

idx = find(ismember(C, 'bla'))

  3 Comments

Nice, just what I was looking for.

And this is faster, too. On my lenovo T460s, a search of a 3000-long cellstring takes about 0.5ms, compared with 2ms with

idx = find(contains(C,'bla'))

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Answer by Jos (10584)
on 25 Feb 2011

So, your original array was a cell array of cells with a single string. Use STRCMP and FIND to get the indices of the cells with a cell containing the specified string

C = { {'a'}, {'b'}, {'c'}, {'a'}, {'a'} } % data
idx = find(strcmp([C{:}], 'a')) % single line engine

  1 Comment

Thanks Jos , It works fine !

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Answer by Jan Simon
on 25 Feb 2011

You can check if your cell is a cell string:

iscellstr(Mycellarray);

This displays the indices and contents of the non-strings:

Index = find(~cellfun('isclass', Mycellarray, 'char'))
disp(Mycellarray(Index));

Another idea is, that some strings are multi-row CHAR matrices:

Index = find(cellfun('size', Mycellarray, 1) > 1)

  0 Comments

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Answer by Omer Moussaffi on 26 Feb 2017

Faster options: count startsWith endsWith

E,g, Index = count(Mycellarray, 'Bla');

  1 Comment

Yes, this method should work well starting from R2016b.

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Answer by Peter Farkas on 9 May 2016

You can also explicitelly define the index matrix:

[rw, ~] = size(cellArray);

ind = [1:1:rw];

idx = strcmp(cellArray, stringToSearchFor);

yourResult = ind(idx);

It is kind of verbose, if you review the code in 2 years time, you will still know what is going on.

  0 Comments

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Answer by Mukesh Jadhav on 9 Oct 2016
Edited by per isakson
on 10 Jan 2017

Haven't tested but this should work fine.

word_to_find=strfind(strarray,'stringtofind');
starray.index(word_to_find);

  0 Comments

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