Re: [R] Collection of lm()s

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Mon, 12 May 2008 14:59:24 +0100 (BST)

On Mon, 12 May 2008, Chip Barnaby wrote:

> Hello,
>
> I would like to create a subscriptable collection (presumably a list) of lm()
> models.
>
> I have a data frame DX containing 6 groups of data. The general idea is (NOT
> RUN) ...
>
> for (i in 1:6)
> { DXS = subset( DX, <whatever>);
> LMX[ i] = lm( <formula>, data = DXS);
> }
>
> Now access model results by subscript ... e.g. coefficients( LMX[ 2]). Or
> would it be [[ 2]]?
>
> I have experimented with various schemes, attempting to "pre-allocate" a list
> etc. without success.

You want

LMX <- list(6)
...
LMX[[1]] <- lm( <formula>, data = DX, subset=<whatever>)

(No trailing ';' needed, [[]] not [] for list elements.)

> Also, I assume that lm() does not make a copy of input data?

It may. This is controlled by the 'model' argument which defaults to TRUE (in recent versions of R: I think it once defaulted to FALSE).

> That is, if I
> want "predict( LMX[ i])", I would have to retain a copy the associated DXS
> subsets?

It does retain the fitted values: see the 'Value' section of ?lm.

>
> TIA,
>
> Chip Barnaby
>
>
>
> ---------------------------------------------------------
> Chip Barnaby cbarnaby_at_wrightsoft.com
> Vice President of Research
> Wrightsoft Corp. 781-862-8719 x118 voice
> 131 Hartwell Ave 781-861-2058 fax
> Lexington, MA 02421 www.wrightsoft.com
>
> ______________________________________________
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>

-- 
Brian D. Ripley,                  ripley_at_stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Mon 12 May 2008 - 14:01:31 GMT

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