[R] merging columns

Chuck White chuckwhite8 at charter.net
Wed Feb 3 03:28:00 CET 2010

Additional clarification: the problem only comes when you have one column selected from the original dataframe.  You need to make the following modification to the original example:

data.df <- data.frame(aa=c(1,1,0), cc=c(1,0,0), aab=c(0,1,0), aac=c(0,0,1), bb=c(1,0,1))

And, the following seems to work:
data.frame(sapply(col2.uniq, function(col) {
  wcol <- which(col==col2)
I had to wrap data.df[,wcol] in another data.frame to handle situations where wcol had one element. Is there a better approach?

---- Chuck White <chuckwhite8 at charter.net> wrote: 
> Hello -- I am trying to merge columns in a dataframe based on substring matches in colnames. I would appreciate if somebody can suggest a faster/cleaner approach (eg. I would have really liked to avoid the if-else piece but rowSums does not like that). Thanks.
> data.df <- data.frame(aa=c(1,1,0), bbcc=c(1,0,0), aab=c(0,1,0), aac=c(0,0,1), bbk=c(1,0,1))
> col2 <- substr(colnames(data.df),1,2)
> col2.uniq <- unique(col2)
> names(col2.uniq) <- col2.uniq
> data.frame(sapply(col2.uniq, function(col) {
>   wcol <- which(col==col2)
>   if(length(wcol)>1) {
>     tmp <- rowSums(data.df[,wcol])
>   } else {
>     tmp <- data.df[,wcol]
>   }
>   as.numeric(tmp>0)
> }))

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