Comments on: Inverse Mapping from Values to Indices

By: Ken Crounse

Ken Crounse — Wed, 06 Sep 2006 21:15:33 +0000

Another one function solution — it’s amazing how many Matlab functions do the same exact thing ;-)

M = interp1(a, 1:numel(a), Minit)

Ken

By: Loren

Loren — Wed, 21 Jun 2006 19:55:49 +0000

Lucio-

Thanks! I should have seen that :-(

–Loren

By: Lucio

Lucio — Wed, 21 Jun 2006 19:45:54 +0000

We can also vectorize loopFR, it looks nicer and a little faster

function M1 = loopFR(M,A)

imap(A) = 1:length(A);
M1 = imap(M);

By: Petr Pošík

Petr Pošík — Thu, 15 Jun 2006 07:31:44 +0000

Hi Loren and blog readers!

There is another simple way of doing that:

function M1 = loopFR(M,A) % loopFR replaces M with its indices from A.

M1 = M;
for i = 1:length(A),
M1(find(M == A(i))) = i;
end

This is, however, not a scalable solution as the number of passes through the matrix M increases with the number of vector A elements. In the tests, it is slightly better than the ismember function, maybe they are implemented in a similar way.

By: Markus

Markus — Wed, 14 Jun 2006 20:42:38 +0000

I suggest to use function cputime for performance measurements, like here:

t0 = cputime;
% evaluate function
dt = cputime – t0;
disp(sprintf(‘Elapsed cpu time = %g seconds.’, dt));

The difference to tic and toc is that here only the cpu time used by Matlab is counted, not that of other running processes.