Looping over column and returning values where conditions are met

I want to loop over a first column (which is column numbers) and return the values when the conditions are met for the next 4 columns. I already have a loop that finds the count of columns that meet conditions but I want it to return the first column values. For example in the image below the highlighted rows are the conditions that are satified and I want to find and reutrn the row numbers (3,5,6 and 9).

[Tommy]

What do you have so far? There are multiple ways you could do this, and looping may not be necessary if you can avoid it

[Joseph McGorry]

count=0;
n=length(matrix);
for k=1:n
  if col2(k)>200 && col2(k)>300 && col3(k)>70
    count=count+1;
  end
end

this is what i have but only counts how many rows meet criteria it doesnt show which row numbers meet the criteria

[Tommy]

If you want/need to keep the loop, you might do something like this:

count=0;
n=length(matrix);
idx=zeros(size(col1));
for k=1:n
  if col2(k)>200 && col2(k)>300 && col3(k)>70
    count=count+1;
    idx(k)=col1(k);
  end
end
idx(~idx)=[];

Answer 1

[James Tursa]

In general, perform find( ) on the condition you want. E.g.,

find(matrix(:,4)>80)

would return the row numbers where the 4th column is greater than 80.

[Joseph McGorry]

Can this be done multiple times for different columns or does it only apply to just one column?

[James Tursa]

E.g.,

find( matrix(:,4)>80 & matrix(:,3)<350 )

would return all row numbers where 4th column is greater than 80 and 3rd column is less than 350. Just be sure to use the single ampersand operator & and not the double ampersand operator &&.

[Joseph McGorry]

Is it also possible to accomplish the same result by using a loop?

[James Tursa]

Sure. If your loop index k is looping over the rows, then you could test within the loop

if( matrix(k,4)>80 & matrix(k,3)<350 )
    % do something
end