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Topic: I'm dense, but...somebody 'splain accumarray() please?
Replies: 23   Last Post: Jul 11, 2013 1:00 PM

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 Kelly Kearney Posts: 24 Registered: 4/25/13
Re: I'm dense, but...somebody 'splain accumarray() please?
Posted: Jul 10, 2013 2:35 PM

> OK, I've managed to write a few answers w/ accumarray and cellfun now; I
> had actually gotten moderately comfortable w/ bsxfun earlier in the
> summer while tutoring an intern long distance...
>
> Now, a slight diversion/extension -- is there any syntax that will
> allow for building a cell array whose contents in each cell are (say) a
> variable-length vector w/ the cell being addressed like accumarray or
> cellfun?
>

I forget how the hell I learned this trick, because the documentation for the SZ input to accumarray is confusing at best (rereading it now, it still doesn't make any sense to me, even knowing what the effect is). Anyway, to get cell array output from your example, add that third input, and make sure your function returns a cell array:

>> a = [1 1 1 2 2 2 2 3 3 3];
>> b = [1 2 3 4 5 8 10 5 6 8];
>> [u,~,c] = unique(a);

>> groups = accumarray(c,b, [length(u) 1], @(x) {x})
>> missing = accumarray(c,b, [length(u) 1], @(x) {setdiff(min(x):max(x), x)})

Date Subject Author
7/5/13 dpb
7/5/13 dpb
7/6/13 james bejon
7/8/13 Steven Lord
7/8/13 dpb
7/9/13 Steven Lord
7/9/13 dpb
7/10/13 Marc
7/10/13 Kim Andrews
7/10/13 dpb
7/10/13 dpb
7/10/13 dpb
7/10/13 EBS
7/10/13 dpb
7/10/13 EBS
7/10/13 dpb
7/10/13 Kelly Kearney
7/10/13 dpb
7/10/13 dpb
7/11/13 Kelly Kearney
7/11/13 dpb
7/10/13 Kelly Kearney
7/10/13 dpb
7/11/13 Steven Lord