CODEWITHSUNDEEP
stringmatlabcell
lara
lara

Reputation: 123

Search a text file for specific words using matlab and add string?

havent been able to find how to search for specific words in a text file anywhere, so here it goes, this is what I have now and just read and prints the entire text file. My Text file contains some words like:

K_G_M_H_NICK_MA,0,7500

P_SA_SWITCH_P_MPE_VL,0,1

If the string begins with 'K' it has to be write 'spec' in the end of the row whatever after K follows. Output has to be then

K_G_M_H_NICK_MA,0,7500 spec

If the string begins with 'P' it has to be write 'test' in the end of the row whatever after P follows. Output has to be then

P_SA_SWITCH_P_MPE_VL,0,1 test

Upvotes: 1

Views: 290

Answers (2)

sco1
sco1

Reputation: 12214

If you have enough memory to load in your entire file, you can take advantage of tools like regexprep to operate on the entire document at once, possibly saving some time both with the comparisons and with the file input/output.

For a regexprep example, we can do something like the following:

% Load entire data file into memory (cell array)
fID =  fopen('mydata.txt', 'r');
tmpdoc = {};
ii = 1;
while ~feof(fid)
    tmpdoc{ii} = fgetl(fID);
    ii = ii + 1;
end
fclose(fID);  % Clean up

% Make the necessary replacements
% String insensitive search
tmpdoc = regexprep(tmpdoc, '(^K.*)$', '$0 spec', 'preservecase'); % Find lines (cells) that begin with K
tmpdoc = regexprep(tmpdoc, '(^P.*)$', '$0 test', 'preservecase'); % Find lines (cells) that begin with P

% Write data
fID_new = fopen('mydata_new.txt', 'w');
fprintf(fID_new, '%s\n', tmpdoc{:});
fclose(fID_new);  % Clean up

For a basic timing with a 2000 line file (just your two lines repeated, which represents a worst case), this approach is roughly 3 times faster than rayryeng's answer, but his approach only took about 0.25 seconds so it's still plenty fast.

Upvotes: 3

rayryeng
rayryeng

Reputation: 104504

MATLAB does not have this capability unfortunately. You don't have a choice but to read in each line of text, check for what you need then save a new file. You can use fgetl to query a line from a text file. Subsequent calls to fgetl reads the next lines and remembers the last line that you read from. You would use this in conjunction with your standard fopen and fclose to open up and close a file. You will need a reference to an open file with fopen before you use fgetl. Assuming that your file is called text.txt, simply read in the line, check the first character for your condition, then print out what you need at the end of the line should it match. It may be wise to also trim any whitespace before and after your code, so strtrim may be useful for you. Something like this should work, also assuming that you want to write to a new file called text_new.txt:

fid = fopen('text.txt', 'r'); % Open up the file
fidw = fopen('text_new.txt', 'w'); % Open up a new file to write

tline = fgetl(fid); % Get the first line in the text file

while ischar(tline) % As long as this line contains characters (i.e. not end of the file)
    % Trim the whitespace
    tline = strtrim(tline);
    % Check if first character is K or k, then write spec at the end of the line
    if tline(1) == 'k' || tline(1) == 'K'
        fprintf(fidw, '%s spec\n', tline);
    % Check if first character is P or p, then write test at the end of the line
    elseif tline(1) == 'p' || tline(1) == 'P'
        fprintf(fidw, '%s test\n', tline);
    % Write the line as is if no conditions match
    else
        fprintf(fidw, '%s\n', tline);
    end

    % Get the next line in the file
    tline = fgetl(fid);
end

% Close the files now
fclose(fid);
fclose(fidw);

Upvotes: 3

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