R help - Jul 2005 - manupulating a data frame column

Could someone tell me how to fix the following error? It looks like
that the reason is that df$x is of the class "factor". Thanks!
> x1<-LETTERS[1:8]; x2<-letters[1:8]; x1[2]<-NA; x1[4]<-NA;
> df<-data.frame(x1=x1, x2=x2)
> idx<-which(is.na(df$x1))
> df[idx,1]<-df[idx,2]
Warning message:
invalid factor level, NAs generated in: "[<-.factor"(`*tmp*`, iseq,
value = c(2, 4))
>

Steven T. wrote:
> Could someone tell me how to fix the following error? It looks like
> that the reason is that df$x is of the class "factor". Thanks!
You are right.

Either don't make it a factor, if you don't want, or try something like 
the following in order to add the relevant levels to df$x1:


x1<-LETTERS[1:8]; x2<-letters[1:8]; x1[2]<-NA; x1[4]<-NA
df<-data.frame(x1=x1, x2=x2)

levels(df$x1) <- c(levels(df$x1), levels(df$x2))

idx<-which(is.na(df$x1))
df[idx,1]<-df[idx,2]


Uwe Ligges
> 
>>x1<-LETTERS[1:8]; x2<-letters[1:8]; x1[2]<-NA; x1[4]<-NA;
>>df<-data.frame(x1=x1, x2=x2)
>>idx<-which(is.na(df$x1))
>>df[idx,1]<-df[idx,2]
> 
> Warning message:
> invalid factor level, NAs generated in: "[<-.factor"(`*tmp*`,
iseq,
> value = c(2, 4))
> 
> 
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