VERY slow for loop

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!

Answer 1

[Walter Roberson]

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.

Answer 2

[sani]

thanks! it reduced to 0.3 sec, amazing!