MATLAB Answers

0

Effective way to extract rows (range) from a text file

Asked by Sultan on 12 May 2019
Latest activity Commented on by Jeremy Hughes on 15 May 2019
I made a small loop to extract rows [range 183:262326] to make a column of 262144x1 column vector. The loop is very inefficient and takes a lot of time to execute. The code is below. Is there any more efficient way ? I dont want to use "Import Data" feature in MATLAB, I want to use code only.
fid=fopen('ABC.txt');
j=1;
for i=183:262326
linenum = i;
C(j,1) = textscan(fid,'%f',1,'delimiter','\n', 'headerlines',i-1);
j = j+1;
end

  2 Comments

Maybe, but you forgot to attach abc.txt so we can't really help very effectively until you do. Maybe dlmread() or importdata() would do the trick, but we don't know until you attach the text file.
Unfortunately the textfile "ABC.txt" is a very large file 25MB even compressing the file proved uselss. But I used the command dlmread() first then used readmatrix() as the former is now not recommended. readmatrix() extracted all the numeric data and output was numeric matrix.

Sign in to comment.

Products


Release

R2019a

2 Answers

Answer by Sultan on 15 May 2019
 Accepted Answer

Unfortunately, due to very large size of "ABC.txt" file, it could not be uploaded. However following the hints of both the commentors. I simply used readmatrix() to extract all the numeric data. The extraction is much efficient.
A = readmatrix('ABC.txt')

  0 Comments

Sign in to comment.


Answer by Jeremy Hughes on 12 May 2019

Readling line by line is quite ineffecient.
Try this:
C = textscan(fid,'%f','delimiter','\n', 'headerlines',182);

  2 Comments

It worked thanks alot, but it is limited to reading only a single row. My intention was to extract the entire column. The problem was solved using readmatrix().
There must be something else in the file other than numbers that causes textscan to stop after the first number.
Glad you found a solution.

Sign in to comment.