MATLAB Answers

VERY slow for loop

24 views (last 30 days)
sani
sani on 18 Jan 2020 at 22:35
Edited: sani on 19 Jan 2020 at 5:49
I have a very slow for loop in my script, it meant to sort a column in a text file (about 500,000 rows) and remove lines with negative values. it took ~10600 sec to finish this lines. Is this normal? any way to improve it?
this is the code:
for i = 1:height (T1(:,2)) %remove negative numbers from column 2
if lt(T1.energy,0)
continue;
else
T1(T1.energy < 0, :) = [];
end
end
thanks!

  0 Comments

Sign in to comment.

Accepted Answer

Walter Roberson
Walter Roberson on 18 Jan 2020 at 22:44
You do not use the variable i inside your for loop, so you are testing the entire energy variable of the table every time through the loop.
if lt(T1.energy,0)
is a vector test, and will only be true if all of the entries in T1.energy are < 0 .
You probably just want,
T1(T1.energy < 0, :) = [];
with no loop -- just the single statement.

  0 Comments

Sign in to comment.

More Answers (1)

sani
sani on 19 Jan 2020 at 5:13
Edited: sani on 19 Jan 2020 at 5:49
thanks! it reduced to 0.3 sec, amazing!

  0 Comments

Sign in to comment.

Sign in to answer this question.