[R] Replacing NAs in one variable with values of another variable

[Ista Zahn]

Hi,

On Tue, Aug 23, 2011 at 12:29 PM, StellathePug <ritacarreira at hotmail.com> wrote:
> Hello everyone,
> I am trying to figure out a way of replacing missing observations in one of
> the variables of a data frame by values of another variable. For example,
> assume my data is X
>
> X <-as.data.frame(matrix(c(9, 6, 1, 3, 9, "NA", "NA","NA","NA","NA",
>                    6, 4, 3,"NA", "NA", "NA", 5, 4, 1, 3), ncol=2))
> names(X)<-c("X1","X2")
>
> I want to change X1 so that instead of the missing values it uses the values
> in X2 (regardless of whether these are missing).

Note that you don't have any missing values in X, as "NA" != NA

So my X1, should become
> X$X1 <- c(9, 6, 1, 3, 9, "NA", 5, 4, 1, 3).
>
> I have searched online for a while and looked at the manuals and the best
> (unsuccessful) attempt I have come up with is
>
> X$X1[X$X1=="NA"] <- X$X2
>
> and that produces the following X1
>
> X$X1<-c(9, 6, 1, 3, 9, 6, "NA", 3, "NA", "NA")
>
> and generates the following warning:
>
> Warning messages:
> 1: In `[<-.factor`(`*tmp*`, X$X1 == "NA", value = c(5L, 3L, 2L, 6L,  :
>  invalid factor level, NAs generated
> 2: In x[...] <- m :
>  number of items to replace is not a multiple of replacement length
>
> I think that my error is that it is ignoring the non-missing values of X1
> and the dimensions don't match. But what I want my code to do is to look at
> the rows of X1, see if it's a missing value; if it is, replace it with the
> value that is in the row of X2; if it's not missing, leave it as is.

Here are two solutions, one that is a correction to your first
attempt, and another using ifelse:

X$X1[X$X1=="NA"] <- X$X2[X$X1=="NA"]

X$X1 <- ifelse(X$X1 == "NA", X$X2, X$X1)


Best,
Ista

>
> What am I doing wrong?
>
> Thank you very much!
> Rita
>
>
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>
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>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org