[R] recode categorial vars into binary data

[Rui Barradas]

Hello,

First of all, you don't need as.data.frame(cbind(...)). It's much better 
to simply do data.frame(...).
As for the conversion, the following function doesn't use randomness but 
gets the job done



df <- data.frame(snr=c(1,2,3,4,5,6,7,8,9,10),
	k1=c(1,1,4,2,3,2,2,5,2,2),
	k2=c(1,2,3,2,1,2,1,3,3,2),
	result=c(4,3,5,4,2,6,4,4,2,3))

fun <- function(x){
	n <- length(x)
	y <- rep(NA, n)
	y[x < median(x)] <- 0
	y[x > median(x)] <- 1
	w <- which(x == median(x))
	y[w[seq_len(n/2 - length(which(x < median(x))))]] <- 0
	y[is.na(y)] <- 1
	y
}

fun(df$k1)
fun(df$k2)



Hope this helps,

Rui Barradas

Em 07-05-2013 17:20, D. Alain escreveu:
> Dear R-List,
>
> I would like to recode categorial variables into binary data, so that all values above median are coded 1 and all values below 0, separating each var into two equally large groups (e.g. good performers = 0 vs. bad performers =1).
>
> I have not succeeded so far in finding a nice solution to do that in R. I thought there might be a better way than ordering each column and recoding the first 50% into 0 and the second into 1. If I use ifelse I have a problem with cases that share the same rank being all median.
>
> e.g.
> df<-as.data.frame(cbind(snr=c(1,2,3,4,5,6,7,8,9,10),k1=c(1,1,4,2,3,2,2,5,2,2),k2=c(1,2,3,2,1,2,1,3,3,2),result=c(4,3,5,4,2,6,4,4,2,3)))
>
> now I want to recode k1 and k2 so that I have half of the values recoded 0 and half recoded 1, split around the median point. The median of k1 is 2 which would lead to unequal groupsize if used 2 as cutoff, so all values k1=2 should be recoded 1 or 0 randomly until both categories have the same length.
>
> something like
>
> df.rec<-as.data.frame(cbind(snr=c(1,2,3,4,5,6,7,8,9,10),k1=c(0,0,1,0,1,1,0,1,0,1),k2=c(0,1,1,0,0,1,0,1,1,0),result=c(4,3,5,4,2,6,4,4,2,3)))
>
> Can anyone help?
>
> Thank you in advance.
>
> Best wishes.
> Alain
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>
>
>
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