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).

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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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Ista Zahn
Sent: Tuesday, August 23, 2011 11:06 AM
To: StellathePug
Cc: r-help at r-project.org
Subject: Re: [R] Replacing NAs in one variable with values of another
variable

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