what is the problem of this function code?

function sectionGrades = extractSection(grades, sectionNumber)

for i = 1 : 7

    if grades(i,2) ~= sectionNumber

      grades(i,:) = [];
    else

    end
end
sectionGrades = grades;
end

it keeps saying Error in extractSection (line 6) if grades(i,2) == sectionNumber

what is wrong with this?

I saved this file as extractSection.m

and 'grades' is a matrix that i downloaded.

Answer 1

[James Tursa]

The reason you are getting the error is because you change the size of the grades variable within the loop, so the last index(es) of the loop are not valid if you have deleted anything. You can fix that a few different ways. One is to run your loop in reverse so that the indexes are always valid. E.g.,

for i = 7 : -1 : 1

Another way is to avoid the loop entirely and just use logical indexing to get the result directly. E.g.,

sectionGrades = grades( grades(:,2)==sectionNumber, : );