Matlab:extract 10000 first lines from a file and write them in a new file

ronald · September 5, 2012, 21:20

Hello,
I have a file "myfile.txt" containing 45000 lines (it is not a matrix). I would like to read the 10000 first lines of my file ( the 10000 first lines define a matrix 3 columns ) and write it in a new txt file name "b.txt". How can I do that ? Please find below the bits of program I have already. Thank you in advance.
Ronald

fid=fopen(' myfile.txt,'r');
N = 10000
for n = 1:N
fgetl(fid);
end

fprintf(fid,'%d %d %d\n','b');
fclose(fid);

GerhardHolzinger · September 6, 2012, 03:53

I did no testing, but shouldn't it look rather like this:

fidRead = fopen('myfile.txt');
fidWrite = fopen('b.txt');

for i=1:N
line = fgetl(fidRead);
writeLine(fidWrite);
end

fclose(fidRead);
fclose(fidWrite);

The code above is some mix of pseudo-code and actual code, but in principle I would do it like this.

Open both files;
read a line and write it right away, repeat this until you are done
Close both files

ronald · September 6, 2012, 19:25

I wrote the program attached below and created a file b.txt with nothing in it in order to fill it with the help of the program ; it gives me the following error message :

"??? Attempted to access writeline(19); index out of bounds because numel(writeLine)=1
Error in ==>prog3 at 12
writeLine(fidWrite)"

Why do I have this error ?
Is it correct to create a file b.txt before launching the program. How can I declare b as a matrix 10000 X 3 in the program ? Thank you.
Ron

fidRead = fopen('myfile.txt','r');
fidWrite = fopen('b.txt','w');
N=10000
for i=1:N
line = fgetl(fidRead);
writeLine(fidWrite);
end
fclose(fidRead);
fclose(fidWrite);

Bernhard · September 7, 2012, 02:33

Supposing you are using Linux, you can easily do this. It seems a bit useless to do it with Matlab.

Code:

$ head a.txt -n 10000 > b.txt

GerhardHolzinger · September 7, 2012, 02:34

as I wrote in my posting, my code contains some pseudocode. There is no function in Matlab called writeLine. Check the matlab help to see how to read and write from files, especially what those function expect as argument.

Depending on how you call fopen() b.txt will be created, will be overwritten or any things you write will be appended if this file exists.

September 5, 2012, 21:20	Matlab:extract 10000 first lines from a file and write them in a new file	#1
ronald New Member ron leco Join Date: Sep 2012 Posts: 2 Rep Power: 0	Hello, I have a file "myfile.txt" containing 45000 lines (it is not a matrix). I would like to read the 10000 first lines of my file ( the 10000 first lines define a matrix 3 columns ) and write it in a new txt file name "b.txt". How can I do that ? Please find below the bits of program I have already. Thank you in advance. Ronald fid=fopen(' myfile.txt,'r'); N = 10000 for n = 1:N fgetl(fid); end fprintf(fid,'%d %d %d\n','b'); fclose(fid);

September 6, 2012, 19:25	writeLine(fidWrite)	#3
ronald New Member ron leco Join Date: Sep 2012 Posts: 2 Rep Power: 0	I wrote the program attached below and created a file b.txt with nothing in it in order to fill it with the help of the program ; it gives me the following error message : "??? Attempted to access writeline(19); index out of bounds because numel(writeLine)=1 Error in ==>prog3 at 12 writeLine(fidWrite)" Why do I have this error ? Is it correct to create a file b.txt before launching the program. How can I declare b as a matrix 10000 X 3 in the program ? Thank you. Ron fidRead = fopen('myfile.txt','r'); fidWrite = fopen('b.txt','w'); N=10000 for i=1:N line = fgetl(fidRead); writeLine(fidWrite); end fclose(fidRead); fclose(fidWrite);

September 7, 2012, 02:33		#4
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 517 Rep Power: 9	Supposing you are using Linux, you can easily do this. It seems a bit useless to do it with Matlab. Code: $ head a.txt -n 10000 > b.txt mturcios777 likes this.

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September 6, 2012, 03:53		#2
GerhardHolzinger Member Gerhard Holzinger Join Date: Feb 2012 Location: Austria Posts: 60 Rep Power: 5	I did no testing, but shouldn't it look rather like this: fidRead = fopen('myfile.txt'); fidWrite = fopen('b.txt'); for i=1:N line = fgetl(fidRead); writeLine(fidWrite); end fclose(fidRead); fclose(fidWrite); The code above is some mix of pseudo-code and actual code, but in principle I would do it like this. Open both files; read a line and write it right away, repeat this until you are done Close both files

September 7, 2012, 02:34		#5
GerhardHolzinger Member Gerhard Holzinger Join Date: Feb 2012 Location: Austria Posts: 60 Rep Power: 5	as I wrote in my posting, my code contains some pseudocode. There is no function in Matlab called writeLine. Check the matlab help to see how to read and write from files, especially what those function expect as argument. Depending on how you call fopen() b.txt will be created, will be overwritten or any things you write will be appended if this file exists.