[R] merging columns

[Matthew Dowle]

Yes.
data.df[,wcol,drop=FALSE]
For an explanation of drop see ?"[.data.frame"

"Chuck White" <chuckwhite8 at charter.net> wrote in message 
news:20100202212800.O8XBU.681696.root at mp11...
> 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)
>  as.numeric(rowSums(data.frame(data.df[,wcol]))>0)
> }))
> 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)
>> }))
>