Help me vectorize this code

for x=1:1:rows

for y=1:1:cols

    RE_p(y,x) = RE(y,x,bestori_map(y,x));

    RO_p(y,x) = RO(y,x,bestori_map(y,x));

end

end

- RE, RO: arrays of size cols*rows*8;

- bestori_map: array of size cols*rows;

what is the best way (and/or fastest) to vectorize this piece of code withouth the need of for cycles ?

Thank you

[Cedric]

What are RE, RO, and bestori_map?

[VisLab]

RE, RO - arrays of size cols*rows*8

bestori_map - array of size cols*rows

Answer 1

[Andrei Bobrov]

s = size(RE);
[ii,jj] = ndgrid(1:s(1),1:s(2));
ij = sub2ind(s,ii(:),jj(:),bestori_map(:));

RE_p = reshape(RE(ij),s(1:2));
RO_p = reshape(RO(ij),s(1:2));

[VisLab]

Works like a charm!

If you'd care to briefly explain the process it would be awesome.

Thank you very much :)

Answer 2

[Walter Roberson]

[X, Y] = ndgrid(1:rows, 1:cols);
X = X(:);
Y = Y(:);
Z = reshape( bestori_map(1:rows,1:cols), [], 1);
linidx = sub2ind(size(RE), X,Y,  Z);
RE_p(1:rows,1:cols ) = reshape(RE(linidx),rows, cols );
linidx = sub2ind(size(RO), X, Y, Z);
RO_p(1:rows,1:cols) = reshape(RO(linidx),rows, cols, );

Note: if RE and RO are the same size then you can re-use linidx instead of re-calculating it.

[Sean de Wolski]

sub2ind()?

[VisLab]

sub2idx() is undefined, and sub2ind() gives me wrong results. Also, RE and RO are both the same size :).

Can you help me a little bit more ? ty

[Andrei Bobrov]

Hi VisLab! Your RO and RE - functions or arrays?

[VisLab]

arrays of cols*rows*8 size (RE,RO) and cols*rows (RE_p,RO_p, bestori_map), respectively.