# [R] matrix logic

Uwe Ligges ligges at statistik.uni-dortmund.de
Wed Jan 11 17:13:58 CET 2006

```t c wrote:

> Uwe,
>   FYI:
>
>   I tried: "data3 <- ifelse(is.na(data1), data2, data1)"
>
>   It seems to me that data3 is an array of length 100.
>
>   I do NOT end up with a dataset of 5 columns and 20 rows.

I have not read carefully enough, for a data.frame you can generalize
the approach as follows:

data.frame(mapply(function(x,y,z) ifelse(is.na(y), z, y),
names(D), D, D2, SIMPLIFY=FALSE))

Uwe Ligges

> Uwe Ligges <ligges at statistik.uni-dortmund.de> wrote:
>   Tom wrote:
>
>>On Tue, 10 Jan 2006 20:25:23 -0500, r user wrote:
>>
>>
>>
>>>I have 2 dataframes, each with 5 columns and 20 rows.
>>>They are called data1 and data2.I wish to create a
>>>third dataframe called data3, also with 5 columns and
>>>20 rows.
>>>
>>>I want data3 to contains the values in data1 when the
>>>value in data1 is not NA. Otherwise it should contain
>>>the values in data2.
>>>
>>>I have tried afew methids, but they do not seem to
>>>work as intended.:
>>>
>>>data3<-ifelse(is.na(data1)=F,data1,data2)
>>>
>>>and
>>>
>>>data3[,]<-ifelse(is.na(data1[,])=F,data1[,],data2[,])
>>>
>
>
> "Better" way is to have the Syntax correct:
>
> data3 <- ifelse(is.na(data1), data2, data1)
>
>
> Please check the archives for almost millions of posts asking more or
> less this question...!
>
>
>
>>Not sure about the bast but...
>>
>>a<-c(1,2,3,NA,5)
>>b<-c(4,4,4,4,4)
>>
>>c<-a
>>c[which(is.na(a))]<-b[which(is.na(a))]
>
>
> Why do you want to know which()?
>
> na <- is.na(a)
> c[na] <- b[na]
>
>
> Uwe Ligges
>
>
>
>>
>>
>>
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>>
>>
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```