How to read line by line a cell file (3x1) using a loop?

Hello,

I have a .txt file. I use the command

regexp(fileread('file1.txt'), '\r?\n', 'split') .';

in order to open it. This file contains 3 lines (it is a 3x1cell). I would like to read line by line each line of this file, by using a loop.

Could anyone help me?

Answer 1

[Ameer Hamza]

For-loop version

fid = fopen('test.txt');

data = {};
while true
    line_data = fgetl(fid);
    if line_data == -1
        break;
    end
    data{end+1} = line_data;
end

data = data';
fclose(fid);

[Ivan Mich]

ok thank you first of all. My qestion is how could i do this by taking only 1st,2nd 3rd line. Eg

I read a file via readtable. From this file I want to take only the two columns of each line.as a result I use commands

t=readtable('test.txt', 'readvariablenames', true);
 o=t{:,2:3}

"o" shows me all lines of two columns I want to use. My question is how I could define the 1st, 2nd and 3rd line separetale by a loop?

[Ameer Hamza]

I couldn't understand the question. Can you attach a small example txt file and show the expected output.

[Ivan Mich]

of course,

Well my .txt file :

point V1 V2 V3 V4 V5 V6 V7

s1 22 36 1 0 5 6 5

s2 47 35 1 0 5 6 5

s3 33 225 1 0 5 6 5

By using o=t{:,2:3} I read all lines of 2nd and 3rd column, I mean

22 36

47 35

33 225

I would like to use a command in order to read 1st,2nd and 3rd line separately.

[Ameer Hamza]

You already have data in variable 'o'. Do you want to read the data in seperate variables?

t=readtable('Files3.txt', 'readvariablenames', true);
o1 = t{:,1};
o2 = t{:,2};
o3 = t{:,3};

Note that in MATLAB, it is recommended not to create separate variables for each column. It is recommended to extract data from the table using indexing.

[Ivan Mich]

By using your solution I can see only value: 22,

I would like to take

o1= 22 36

o2= 47 35

o3= 33 325

How could I take it?

[Ameer Hamza]

Ok. I get it now. Please try

t=readtable('Files3.txt', 'readvariablenames', true);
o1 = t{1,2:3};
o2 = t{2,2:3};
o3 = t{3,2:3};

[Ivan Mich]

οκ , Thank you. May I ask you something ? If I want to use a loop, when I use

for i=1:numel(o)

and when

    for i=1:nrows(o)

?

Which is the most correct?

[Ameer Hamza]

The method with for loop is quite messy if you want to use different variable names

t=readtable('Files3.txt', 'readvariablenames', true);

o1 = zeros(1,2);
o2 = zeros(1,2);
o3 = zeros(1,2);
for i=1:size(t,1)
    for j=2:3
        if i==1
            o1(j-1) = t{i,j};
        elseif i==2
            o2(j-1) = t{i,j};
        elseif i==3
            o3(j-1) = t{i,j};
        end
    end
end

The same can be done with the following code, but it uses eval(), which is highly unrecommended (or borderline prohibited).

t=readtable('Files3.txt', 'readvariablenames', true);
for i=1:size(t,1)
    eval(sprintf('o%d=t{%d,2:3};', i, i));
end

[Ivan Mich]

Οκ , thank you. The reason I am asking you these questions is that I want to make a code for a problem

Imagine that I have File3.txt, File2.txt and one .exe file (lets call it my.exe). File3.txt has my data, File2.txt is the input of my.exe(input that is needed in order to execute my.exe).

I would like from file3 to take only one line and put in a specific line of the file2(input). After putting this line in file2 I can run my exe file. The problem is that File 3 obtain many lines. I want to use o for loop in order to run my .exe file for all the lines separately of file3 (I mean I would like to take the first line of 2nd and 3rd column from file 3, put this line to file2, run my.exe file and take my results. After that I would like to take the second line of 2nd and 3rd column from file 3, put this line to file2, run my.exe file and take my results. After all this repeatability I would like to the last line of 2nd and 3rd column of file 3 put this line to file2, run my.exe file and take my results.)

I have to mention that I want after each repeatability the name of input file (File2.txt) does not change, inspite of the different content.

I wrote some commands but I can't continue it to composition.

%for 
% for j= 1: size{lines_to_replace_with,1}
% 
% line_to_replace_withnew = sprintf('%g\t%g',lines_to_replace_with(j));
% end 
t3 = readtable('Files3.txt', 'readvariablenames', true);
nrow = size(t3,1);
lines2 = regexp(fileread('File2.txt'), '\r?\n', 'split') .';
for K = 1 : nrow
   line_to_replace_with = sprintf('%g\t%g',t3{K,2:3});
   replaced_lines = [lines2(1:2); line_to_replace_with; lines2(4:end)];
   newfilename = sprintf('newfile%d.txt', K);
   fid = fopen(newfilename, 'wt');
   fprintf(fid, '%s\n', replaced_lines{:});
   fclose(fid);
end
system('my.exe <File2.txt')

Do you have any idea?

[Ameer Hamza]

You already got the idea of getting information out of file3. The easiest way I can think of is to load the entire file2.txt, split it into lines, and insert the data at the required location. Then save the new data in file file4.txt and input file4.txt to the my.exe.

[Ivan Mich]

Excuse me but I am confused, because I have tried the previous code and it works only for the first line of the data of File3.txt. My biggest problem is that I can not compose the loop that my code needs in order to make it run and take the results that I want. I would appreciate it if you could tell me how to run my script because I am really confused...

[Ameer Hamza]

Ivan, can you attach two files txt (preferably with the minimum number of lines to explain the concept). Also, explain what do you want the content of file2.txt after each iteration. It will make it easy for me to suggest a solution. Right now, I can only guess the required behavior, and it may not be what you want at the end.

[Ivan Mich]

of course. I will upload these two files: "File2.txt" is the input of the my.exe file. and "Files3.txt" has my data. I would like to take numbers of 2nd and 3rd column of first line of "Files3.txt" and put it to line3 of File2.txt. File2.txt is the input of .exe file. That' s why I use commands

line_to_replace_with = sprintf('%g\t%g',t3{K,2:3});
   replaced_lines = [lines2(1:2); line_to_replace_with; lines2(4:end)];
   newfilename = sprintf('newfile%d.txt', K);
   fid = fopen(newfilename, 'wt');
   fprintf(fid, '%s\n', replaced_lines{:});
   fclose(fid);

after making this replacement I would like execute the .exe file , that's why i use command

system('my.exe <File2.txt')

After execiting this programm (I mean "my.exe" file) I would like to take numbers of 2nd and 3rd column of second line of Files3.txt and put it to line3 of File2.txt. After replacement I would like execute the .exe file and taking my results (and save them)

After that, I would like to take numbers of 2nd and 3rd column of third line of Files3.txt and put it to line3 of File2.txt. After replacement I would like execute the .exe file and taking my results (and save them).

I have to mention that I want after each repeatability the name of input file (File2.txt) does not change, inspite of the different content (and save them).

To be more spesific, for the first iteration File 2 has this content:

there are several values

the problem is

22 36

there are several values

the problem is

there are several values

the problem is

For the second iteration File2.txt has this content:

there are several values

the problem is

47 35

there are several values

the problem is

there are several values

the problem is

And for the third and the last iteration File2 has this content:

there are several values

the problem is

33 225

there are several values

the problem is

there are several values

the problem is

I wrote some commands but I can't continue it to composition of the loop I would like to make.

I have to mention that it is very important to keep the name of "File2.txt" as "File2.txt" , I mean that the name does not have to be changed.

I hope I help you with my explaination.

[Ameer Hamza]

Try this. There might be a more efficient way to read and write the file, but this is the simplest way I can think of.

data_f3 = readtable('Files3.txt');
data_f3 = data_f3{:, 2:3};

for i=1:size(data_f3,1)
    f = fopen('File2.txt', 'r');
    data_f2 = textscan(f, '%s', 'Delimiter', '\n');
    fclose(f);
    data_f2 = data_f2{1};
    data_f2{3} = num2str(data_f3(i,:));
    f = fopen('File2.txt', 'w');
    fprintf(f, '%s\n', data_f2{1:end-1});
    fprintf(f, '%s', data_f2{end});
    fclose(f);
    system('my.exe < File2.txt')
end

[Ivan Mich]

Ok , thank you first of all. Also I would like to ask something more. Files3.txt has a 4th column right (this column has numbers content). Could I use command if in order to read line by line the numbers of 4th column and after that to replace sepcific numbers?

to be more specific, I would like to put specific lines in input file, depending on the number of 4th column?

Is there a way to put command if after command

for i=1:size(data_f3,1)

???

for example I would like to ewrite:

    
if data_f3{:,4}==0
do something
else
do something
end

could you help me?

[Ameer Hamza]

Your idea seems to be correct. My code already shows how to replace the line in file2.txt. You can use an if-else block to decide what you want to do based on the element in the fourth column.

[Ivan Mich]

ok, my question is do I have to put an extra for ?

i mean

for i=1:size(data_f3,1)
    for ii=1:size(data_f3{:,4},1)
        if data_f3{:,4}==0
do something
else
do something
end
    end
end

or it is not necessary because the number of lines is the same?

Do you understand what I mean?

[Ameer Hamza]

I think using single for loop should be fine. Something like this

for i=1:size(data_f3,1)
    if data_f3{i,4}==0
        do something
    else
        do something
    end
end