I have two matrices:
a: (0.5 0.5; 0.3 0.7)
idx: ((0 0);(0 1);(1 1))
I want to use the idx as i and j pairs to get the values out of a. In longform, this would be:
a[0;0]
a[0;1]
a[1;1]
Currently, when I try to index it as a idx, it behaves as if I've entered a[0 0] etc.
What am I doing wrong?
Apply Each Right (@kylebonnes) is the correct answer to OP. You might prefer an alternative approach to scattered indexing if it suited you better to represent a as a vector.
q)M:2 2#V:5 5 3 7%10 / matrix; vector
q)r:0 0 1;c:0 1 1 / rows; columns
q)M ./:r,'c
0.5 0.5 0.7
q)V 0 2 sv(r;c) / index V as if it were M
0.5 0.5 0.7
Here the left argument sv specifies a (variable) arithmetic base. For rows r and columns c you can use (0,N)sv(r;c) as indexes into a razed N-column matrix.
q)show A:4 5#B:"the quickbrownfox "
"the "
"quick"
"brown"
"fox "
q)rc:6 2#2 0 2 1 1 1 2 4 1 3 0 1
q)A ./: rc
"brunch"
q)B 0 5 sv flip rc
"brunch"