[R] Setting elements in data frame

[Kaspar Pflugshaupt]

On Thursday 22 February 2001 15:29, Peter Dalgaard BSA wrote:


> Hmmmm... How about
>
> recode<-function(x,value,replacement){
> 	x[if (is.na(value)) is.na(x) else x==value] <- replacement
> 	x
> }
> s <-sapply(x,is.numeric)
> x[s] <- lapply(x[s], recode, 6, 6000)
> x[s] <- lapply(x[s], recode, NA, 1000)

Getting better and better!

While we're at it: Why would the following not work (it's the first version I 
tried):

  data.frame(lapply(x,function(z) ifelse(z==6,6000,z)))

It does the replacement all right, but the factor column gets converted to 
integer. Looking at ?ifelse, I find that 

     `ifelse' returns a value with the same shape as `test' which is
     filled with elements selected from either `yes' or `no' depending
     on whether the element of `test' is `TRUE' or `FALSE'. If `yes' or
     `no' are too short, their elements are recycled.

So could it be that because 6 (an integer) is present in the comparison, the 
result _will_ be integer no matter what class z is? The help doesn't say so, 
but I might overlook something basic. Still, checking this out:

> data.frame(lapply(x,function(x) ifelse(x==6.0,6000.0,x)))  
# would give float results, if above were true
  S1   N1   N2
1  2    2 6000
2  3    4   NA
3  4 6000    0
4  1    9 6000

still gives integer results. And the problem does not lie with the data.frame 
conversion: 

> str(lapply(x, function(x) ifelse(x==6,6000,x)))
List of 3
 $ S1: int [1:4] 2 3 4 1
 $ N1: num [1:4] 2 4 6000 9
 $ N2: num [1:4] 6000 NA 0 6000



puzzled-ly yours


Kaspar Pflugshaupt

-- 


Kaspar Pflugshaupt
Geobotanical Institute
ETH Zurich, Switzerland

http://www.geobot.umnw.ethz.ch
mailto:pflugshaupt at geobot.umnw.ethz.ch
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