[R] Creating a new column from a series of columns

[Jeff Newmiller]

This method handles cases where multiple columns are "Yes".

library(reshape2)
ddl <- melt( dd, id.vars = "PLTID" )
ddl[ is.na( ddl$value ), "value" ] <- ""
ddl <- ddl[ "Yes" == ddl$value, ]
result <- merge( dd[ , "PLTID", drop=FALSE ]
                , ddl[ , c( "PLTID", "variable", "value" ) ]
                     , all.x=TRUE
                )

On Fri, 31 Oct 2014, Fisher Dennis wrote:

> R 3.1.1
> OS X
>
> Colleagues,
> I have a dataset containing multiple columns indicating race for subjects in a clinical trial.  A subset of the data (obtained with dput) is shown here:
>
> structure(list(PLTID = c(7157, 8138, 8150, 9112, 9114, 9115,
> 9124, 9133, 9141, 9144, 9148, 12110, 12111, 12116, 12134, 12136,
> 12137, 12142, 12143, 12146, 12147, 13159), Indian..RACE1. = c(NA,
> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,
> NA, NA, NA, NA, NA), Asian..RACE2. = c("", "Yes", "", "", "",
> "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "",
> ""), Black..RACE3. = c("Yes", "", "", "Yes", "Yes", "Yes", "Yes",
> "Yes", "", "Yes", "", "", "", "", "", "", "", "Yes", "Yes", "",
> "", ""), Native.Hawaiian.or.other.Pacif..RACE4. = c(NA, NA, NA,
> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,
> NA, NA, NA), White..RACE5. = c("", "", "Yes", "", "", "", "",
> "", "Yes", "", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes", "Yes",
> "", "", "Yes", "Yes", "Yes"), Other.Race..RACE6. = c(NA, NA,
> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,
> NA, NA, NA, NA), Specify.Other.Race..RACEOTH. = c(NA, NA, NA,
> NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA,
> NA, NA, NA)), .Names = c("PLTID", "Indian..RACE1.", "Asian..RACE2.",
> "Black..RACE3.", "Native.Hawaiian.or.other.Pacif..RACE4.", "White..RACE5.",
> "Other.Race..RACE6.", "Specify.Other.Race..RACEOTH."), class = "data.frame", row.names = 43:64)
>
> I would like to add a column that indicates which of the other columns contains ?Yes?.  In other words, that column would contain:
> 	Black..RACE3.
> 	Asian..RACE2.
> 	White..RACE5.
> 	Black..RACE3.
> 	?
>
> Even better would be
> 	Black
> 	Asian
> 	White
> 	Black
> 	?
> (which I can accomplish with strsplit)
>
> None of the rows contains more than one ?Yes? although it is possible that none of the entries in a row would be ?Yes? (in which case, the entry in the new column should be NA)
>
> I could do this by looping through each of the columns with something like this:
> 	DATA$RACE	 	<- NA
> 	for (COL in 2:8)	DATA$RACE[which(DATA[,COL] == "Yes")]	<- names(DATA)[COL]
> But, I suspect that there is some more elegant way to accomplish this.
>
> Thanks in advance.
>
> Dennis
>
> Dennis Fisher MD
> P < (The "P Less Than" Company)
> Phone: 1-866-PLessThan (1-866-753-7784)
> Fax: 1-866-PLessThan (1-866-753-7784)
> www.PLessThan.com
>
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> and provide commented, minimal, self-contained, reproducible code.
>

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