Find a string inside another string in Matlab

Question

I have to creade a function that takes two inputs: a cell array of strings (let's call it txt) and a single string (let's call it str). The function has to remove each element of the cell vector txt whose string is either identical to str or contains str as a substring. For the moment I've tried with the following:

function c = censor( txt,str )
    c = txt;
    n = length(c);
    for i = 1:n
        a = c{ i };
        a( a == str ) = [];
        c{i} = a;
    end
end

But it doesn't work, it gives the error that Matrix dimensions must agree. I understand that it might be because str has more than one character, but I don't know how to find if str is contained in any of the strings of the cell array txt.

Take a look at strfind. se.mathworks.com/help/matlab/ref/strfind.html — Anders Schou
– Anders Schou, Commented May 21, 2015 at 12:16
Nice, it does what I need, but the problem is when the coincidence appears more than one time. I don't know how to remove each element once I find all the coincidences. — Hec46
– Hec46, Commented May 21, 2015 at 12:33

Ben · Accepted Answer · 2015-05-21 12:25:55Z

3

As Anders pointed out, you want to use strfind to look for strings inside other strings. Here is a way you could write your function. Basically apply strfind on the whole txt cell array, and then remove entries in which there was a match.

Code:

function censor(txt,str)
clc
clear

%// If no input are supplied..demo
if nargin ==0

    str = 'hello';
    txt = {'hellothere' 'matlab' 'helloyou' 'who are you' 'hello world'};
end

IsItThere = strfind(txt,str)

Now IsItThere is a cell array with some 1's and empty cells:

IsItThere = 

    [1]    []    [1]    []    [1]

Let's fill empty cells with 0, so we can perform logical indexing later:

IsItThere(cellfun('isempty',IsItThere))={0}

Find the indices in which a match occured:

IndicesToRemove = find(cell2mat(IsItThere))

IndicesToRemove =

     1     3     5

And remove cells:

txt(IndicesToRemove) = [];

txt now looks like this:

txt = 

    'matlab'    'who are you'

end

You can combine a few steps together if you like, but I hope that was clear enough :)

Here is the whole code that you can copy/paste in a .m file:

function censor(txt,str)
clc
clear

%// If no input are supplied..demo
if nargin ==0

    str = 'hello';
    txt = {'hellothere' 'matlab' 'helloyou' 'who are you' 'hello world'};
end

IsItThere = strfind(txt,str)

IsItThere(cellfun('isempty',IsItThere))={0}

IndicesToRemove = find(cell2mat(IsItThere))

txt(IndicesToRemove) = [];
txt
end

answered May 21, 2015 at 12:25

Ben

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2 Comments

Hec46 Over a year ago

Your method works with your example but for some reason it does not work when each element of the cell array is a sentence and str appears more than once. Any idea on how to improve this method? It is really good but I don't know how to make it work for sentences with more than one coincidence. For example, using the first 8 lines of the US national anthem and str = 'the', I get: IsItThere = [24] [30] [43] [6] [1x2 double] [1x2 double] [0] [1x4 double]

Anders Schou Over a year ago

@Hec46 When there are multiple occurrences strfind gives the index where the str starts. You can use something like IsItThere(~cellfun('isempty', IsItThere)) = {1} before IsItThere(cellfun('isempty', IsItThere)) = {0}

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