What are some good ways to emulate cascading indexing in MATLAB?

Question

E.g. I would like to do things such as:

A=4:20;
find(A>5)(2) % want to access the 2nd element of the index array returned by find

I just thought of an alternative solution, and updated my answer. Anyway, it's certainly not the first time something similar has been asked, but... http://blog.stackoverflow.com/2010/11/dr-strangedupe-or-how-i-learned-to-stop-worrying-and-love-duplication/ — chappjc, Oct 10 '13 at 22:35

score 3 · Accepted Answer · edited May 23 '17 at 10:30

3

Yes, this comes up fairly frequently in different contexts, and the one-line answer is subsref. For your case, it is this:

subsref(find(A>5),struct('type','()','subs',{{2}}))

A much cleaner solution uses an undocumented builtin:

builtin('_paren',find(A>5),2)

As an alternative to ugly syntax or undocumented functionality, you could define a small function like the following,

function outarray = nextind(inarray,inds)
outarray = inarray(inds);

Or an inline function:

nextind = @(v,ii) v(ii);

And call it like nextind(find(A>5),2). This is cleaner than subsref and good if you are doing linear indexing (not subscripts).

edited May 23 '17 at 10:30

Community

answered Oct 10 '13 at 20:53

chappjc

1

Not helpful, I guess. Oh, well – chappjc Oct 11 '13 at 15:30
hmm yeah I don't understand the -1 either. I wish the person who downvoted added a comment. Anyway, thanks for your answer! – Franck Dernoncourt Oct 15 '13 at 20:52
It's probably because of the duplication factor... but that's why I added all the links and an alternate solution. – chappjc Oct 15 '13 at 21:04

1 Answers1