[R] Merging factor levels.

[Prof Brian D Ripley]

On Mon, 12 Nov 2001, [iso-8859-1] Göran Broström wrote:

> This must be a FAQ, but I can't find the answer:
> I have a factor 'okk':
>
> > table(okk)
> okk
>      Other   STORKAGE SKELLEFTEA    FALMARK       BOLE  NEAR_TOWN
>      14064        560        346        526        332         34
>
> Now I want to put the cases in 'NEAR_TOWN' into the 'Other' category',
> so I try:
>
> > okk <- ifelse(okk == "NEAR_TOWN", "Other", okk)
> > table(okk)
> okk
>     1     2     3     4     5 Other
> 14064   560   346   526   332    34
> > is.factor(okk)
> [1] FALSE
>
> This is not what I intended. I can do what I want the hard way (i.e., by
> converting  okk  to character an then back again) but there
> must be something simpler?

Something like

levels(okk) <- c(levels(okk)[1:5], "Other")

If you set two levels to be the same label, they get merged.

-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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