how to assign variables to an array to unknown length

Question

I've created an empty array with the name pattern and now I am reading a file that generates strings and each string I want to be saved in a variable p. I want the pattern to be displayed on the MATLAB command window. The line assigned to P should be stored in array pattern.

pattern=[]
while ~isnan(l)
        p=fgetl(fp);
pattern=(pattern,p[])
end

Can you help, I think I am doing it wrong to assign pattern. Because it wouldn't get the result

pattern = [];
while(~feof(fid))
    l = fgetl(fid);
    idx = regexp(l, '^information$');
    if size(idx,1)>0
        l = fgetl(fid); 
        while ~isnan(l)
            p = fgetl(fid);
        end 
    end
end

The above is the code

Please provide a functioning example so we can best answer your question. For variable length strings I would advise using a cell array. Also, concatenating arrays in every iteration of a loop is highly inefficient, consider preallocating the cell array for speed. — sco1
– sco1, Commented Aug 20, 2014 at 12:46

Stewie Griffin · Accepted Answer · 2014-08-20 13:13:27Z

2

You need to use cells for this, thus the correct type of brackets is {}, not []. When the entire text is saved in a cell array, you can display it using a combination of cellfun and disp.

Something like this should work:

fid = fopen('textfile.txt');

p = fgetl(fid);
pattern = {p}
while ischar(p)
    p = fgetl(fid);
    pattern = [pattern; {p}];
end

fclose(fid);
cellfun(@disp, pattern)

edited Aug 20, 2014 at 13:13

answered Aug 20, 2014 at 12:57

Stewie Griffin

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6 Comments

Samiya Qureshi Over a year ago

It says variable pattern appears to change size on every loop iteration. Consider p reallocating for speed

rayryeng Over a year ago

Minor comment (even though this solution is awesome). What about using celldisp for displaying cells?

rayryeng Over a year ago

@SamiyaQureshi - That is expected. The size of the cell array is changing at each iteration. What you are asking can't be done with pre-allocation.

Stewie Griffin Over a year ago

@rayryeng, I don't think celldisp works well for this as the result will be: pattern{1} = (linebreak) function why(n) (linebreak) pattern{2} = (linebreak) etc. Thanks though =)

rayryeng Over a year ago

@RobertP. - Oh well I tried! You're welcome :) +1 btw.

|

zinjaai · Accepted Answer · 2014-08-20 12:50:43Z

1

if your strings have different length, then you should save them in a cell array.

%// create empty cell array
pattern=cell(0) 

while ~isnan(l)
    p=fgetl(fp);

    %// save in cell array
    pattern{end+1} = p

    %// show in command window
    disp(p) 
end

now you can access your first pattern with pattern{1} and your second with pattern{2}...

answered Aug 20, 2014 at 12:50

zinjaai

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