A compact way to find max in one column with a condition on the second column

Given

a = [35   -1
    21     1
    11     2];

I want the max in the first column, but the max cannot be that one where there is a "-1" in the second column.

Therefore the correct answer is not "35" (since in the second column there is "-1"), but "21".

Do you know a compact way to get this max in the first column, with the condition on the second column ?

Answer 1

[Bruno Luong]

a = [35   -1
    21     1
    11     2];
max(a(a(:,2) ~= -1,1))

ans = 21

[Sim]

thanks a lot @Bruno Luong! :-)

And....if I want to know the row's index of "a" where there is the max, i.e. "21" ?

The following gives me index equal to "1" (i.e. the first row) instead of "2" (i.e. the second row)..

a = [35   -1
    21     1
    11     2];
[max_a, idx_max_a] = max(a(a(:,2) ~= -1,1))

max_a = 21

idx_max_a = 1

[Bruno Luong]

If you want to get row index of the max value:

a = [35   -1
    21     1
    11     2];
filteridx = find(a(:,2) ~= -1);
[maxvalue, maxidx] = max(a(filteridx,1));
maxidx = filteridx(maxidx)

maxidx = 2

[Sim]

thanks a lot! :-)