[R] "factorise" variables in a data.frame

[baptiste auguie]

Excellent!

I felt it was fairly trivial but i can be quite dense on Friday  
mornings.

I really like the generalisation.

Many thanks,

baptiste


On 3 Apr 2009, at 12:11, Wacek Kusnierczyk wrote:

> baptiste auguie wrote:
>> Dear list,
>>
>> I often need to convert several variables from numeric or integer  
>> into
>> factors (before plotting, for instance), as in the following example,
>>
>>
>> d <- data.frame(
>>    x = seq(1, 10),
>>    y = seq(1, 10),
>>    z = rnorm(10),
>>    a = letters[1:10])
>>
>>
>> d2 <-
>> within(d, {
>>    x = factor(x)
>>    y = factor(y)
>>     })
>>
>> str(d)
>> str(d2)
>>
>>
>> I'd like to write a function factorise() which takes a data.frame and
>> a vector of variable names, and returns the original data.frame with
>> the desired variables converted to factor,
>>
>
> would this not be good enough:
>
>    # dummy data
>    data = data.frame(x=1:10, y=1:10)
>
>    # a factorizer
>    factorize = function(data, columns=names(data)) {
>       data[columns] = lapply(data[columns], as.factor)
>       data }
>
>    sapply(factorize(data, 'x'), is)
>    # $x "factor" ...
>    # $y "integer" ...
>    lapply(factorize(data), is)
>    # $x "factor" ...
>    # $y "factor" ...
>
>
>> factorise <- function(d, f)
>> ***ply(d, f, factor) # some apply function
>>
>> also, perhaps a defactorise() function doing the reverse operation
>> with as.numeric.
>
> then, perhaps,
>
>    # an izer
>    ize = function(data, columns=names(data), izer=as.factor) {
>       data[columns] = lapply(data[columns], izer)
>       data }
>
>    ize(data, 'x', as.logical)
>
> or even
>
>    ize = function(izer)
>       function(data, columns=names(data)) {
>          data[columns] = lapply(data[columns], izer)
>          data }
>
>    logicalize = ize(as.logical)
>    characterize = ize(as.character)
>
>    lapply(logicalize(data), is)
>    # $x "logical" ...
>    # $y "logical" ...
>    lapply(characterize(data, 'x'), is)
>    # $x "character" ...
>    # $y "integer" ...
>
> etc.
>
> vQ
>
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_____________________________

Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag