match a word/string

Hi all. I have a file, in which the first column which contains 27k rows of words/strings. (eg:GDD51). I need to search a particular string and create another file with all values corresponding to the second column in that file. The problem is, i can't search for a string. It says error! Can someone help me. this is the code i used:

    x=0;
    for i=1:27099
        if file(i,1)=='GDD51
            x=x+1;
            newfile(x,1)=file(i,2);
        end
    end

And i get this error: Undefined function 'eq' for input arguments of type 'table'. Please help,Thanks

[Geoff Hayes]

Bharat - please post the code that you are using to read the data from file, and search for the string that you are interested in. As well, since there is an error, please post the full error message (all text in red). Just update/edit your above question with thus additional information.

[Bharat]

Sorry Geoff, I am new to matlab and this site. I apologize that I didn't post the query properly.

[Image Analyst]

Well you didn't have a closing apostrophe on the "if" line. But why not just use my answer?

Answer 1

[per isakson]

if file(i,1)=='GDD51' &nbsp will not work for two reasons

Firstly, the comparison is made position by position. The result is a vector of logical. To assert identical strings all must be true.

    >> 'ABC'=='AAA'
    ans =
         1     0     0

    >> all( 'ABC'=='AAA' )
    ans =
         0

However,&nbsp if&nbsp of recent Matlab versions applies an implicit&nbsp all. &nbsp That was not always the case(?). See if, elseif, else

    [...] An expression is true when its result is nonempty and contains 
    only nonzero elements (logical or real numeric).

Secondly, the strings must have the same length else an error is thrown

    >> 'ABC'=='AABCA'
    Error using  == 
    Matrix dimensions must agree.

I think, the best code is (not tested)

    >> newfile = file( strcmp( 'GDD51', file(:,1) ), 2 );

[Bharat]

thanks per isakson! I actually still used the for loop but with strcmp!

[Image Analyst]

Any reason why you chose not to use ismember(), which is how I think most MATLABers would do it?

[per isakson]

According to my old rule of thumb

    ism = strcmp( str, cell_array_of_strings );

is significantly faster than

    ism = ismember( str, cell_array_of_strings );

(This is a special case to ismember)

However, that might have changed.

Answer 2

[Image Analyst]

Try this:

% Create sample data
cellArrayOfStrings = {'No Match this index', 'GDD51', 'no match here either'};
% Find index where cell contents = 'GDD51'
index = ismember(cellArrayOfStrings, 'GDD51')

[Image Analyst]

Regarding your edit for making a file of the second column where it's true

fid = fopen(filename, 'wt');
for k = 1 : length(index)
  if index(k)
      fprintf(fid, '%s\n', cellArrayOfStrings{k});
  end
end
fclose(fid);