With rows have a -1 in its third column? (matlab)

Question

Let me explain my question with an example.

I have the matrix

$\begin{pmatrix}0 &5 &1 \\ 0&5&-1 \\ 10&-55&2 \\ 4&0&-1 \\ 1&1&1 \\\end{pmatrix}$

and I need to know the number of each row that has a $-1$ in its third column.

How I can do this efficiently?

Thanks!

something like sum(find(A(:3) + 1))? – mookid Mar 26 '14 at 01:27 — mookid, Mar 26 '14 at 01:27
yea, the find command works perfect ;) – yemino Mar 26 '14 at 01:39 — yemino, Mar 26 '14 at 01:39
sum(A(:,3)) or nnz(A(:,3)) will probably be faster – Luis Mendo Mar 27 '14 at 09:38 — Luis Mendo, Mar 27 '14 at 09:38

score 1 · Answer 1 · answered Mar 26 '14 at 01:41

1

Inspired in the mookid answer, the solution is:

find(A(:,3)==-1)

Thanks!

answered Mar 26 '14 at 01:41

yemino

1 Answers1