[Fwd: Re: [R] reduce levels]

[Paul Johnson <>]

Somebody was asking about how to change a whole dataset or collection of 
variables into factors without doing it one at a time.  Here's an answer 
from r-help

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Paul E. Johnson                       email: pauljohn_AT_ku.edu
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• To: Bill.Venables_AT_csiro.au
• Subject: Re: [R] reduce levels
• From: Claus Atzenbeck <>
• Date: Tue, 8 Nov 2005 18:10:02 +0100 (CET)
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On Tue, 8 Nov 2005 Bill.Venables_AT_csiro.au wrote:

> sub$mm <- factor(sub$mm)

Great. This is exactly what I need.

> is the simplest way to change a single factor in this way.  To do a
> whole data frame you just need a loop:
>
> drop_unused_levels <- function(data)
> 	as.data.frame(lapply(data, function(x) if(is.factor(x))
> factor(x) else x ))

Thanks for this additional information. Maybe I'll be in need of it
later.

Greetings,
Claus

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