R help - Aug 2011 - Replacing NAs in one variable with values of another variable

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). 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.

What am I doing wrong?

Thank you very much!
Rita


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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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> View this message in context:
http://r.789695.n4.nabble.com/Replacing-NAs-in-one-variable-with-values-of-another-variable-tp3763269p3763269.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


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

Thank you Dan and Ista!

Both of you are correct, I should have used NA rather than "NA" in my
example. So the correct code should be:

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")      

X$X1[is.na(X$X1)] <- X$X2[is.na(X$X1)] 

Where the last line replaces the missing observations of X1 by those of X2.
The "if else" statement also works.

Thank you very much, again!
Rita

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