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Re: Applying function to vector by index
From: |
Paul Kienzle |
Subject: |
Re: Applying function to vector by index |
Date: |
Mon, 9 Dec 2002 11:56:46 -0500 |
User-agent: |
Mutt/1.2.5.1i |
Iago,
Sparse matrices are a likely candidate here. Split your data with
one column per bin:
n = length(d);
S = sparse(1:n,idx,d);
Then the stats are:
count = spsum(sparse(1:n,idx,1));
mean = spsum(S) ./ count;
var = spsum( (S - sparse(1:n,idx,mean(idx))).^2 ) ./ (count-1);
Not as good as a generic split/apply operations I agree, but even
with split/apply performance wouldn't be much better than a loop since
you would still be interpreting var(x) for each bin separately.
Paul Kienzle
address@hidden
On Mon, Dec 09, 2002 at 04:22:17PM -0000, Iago Mosqueira wrote:
> Hi,
>
> I have a long vector classified in ten bins of different length according to
> another vector. I want to estimate the variance, or any other function, of
> the values from the first vector for each of the categories described by the
> second, without using a loop. Is there any obvious way of doing this I am
> overlooking? In R one could do
>
> sapply(split(d,idx),var)
>
> where d is my data vector and idx the index vector.
>
> Many thanks,
>
>
> iago
>
>
>
>
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Octave is freely available under the terms of the GNU GPL.
Octave's home on the web: http://www.octave.org
How to fund new projects: http://www.octave.org/funding.html
Subscription information: http://www.octave.org/archive.html
-------------------------------------------------------------
- Applying function to vector by index, Iago Mosqueira, 2002/12/09
- Re: Applying function to vector by index, Mike Miller, 2002/12/09
- Re: Applying function to vector by index,
Paul Kienzle <=
- Re: Applying function to vector by index, Iago Mosqueira, 2002/12/09
- Re: Applying function to vector by index, Paul Kienzle, 2002/12/09
- Re: Applying function to vector by index, Paul Kienzle, 2002/12/09
- Re: Applying function to vector by index, Andy Adler, 2002/12/09
- Re: Applying function to vector by index, Schloegl Alois, 2002/12/10
- Re: Applying function to vector by index, Paul Kienzle, 2002/12/12
- Re: Applying function to vector by index, Andy Adler, 2002/12/12
- Re: Applying function to vector by index, Schloegl Alois, 2002/12/12
- Re: Applying function to vector by index, Paul Kienzle, 2002/12/12
- Re: Applying function to vector by index, Andy Adler, 2002/12/12