# [R] a strange behavior with ifelse

jim holtman jholtman at gmail.com
Sat Apr 9 04:07:38 CEST 2011

```try this:

>  a=c(2,NA,NA,NA,2,2,NA,2,NA,2)
>  b=c(NA,1,1,NA,2,2,2,2,2,2)
>  c1 <- ifelse((!is.na(a) & a == 1) | (!is.na(b) & b == 1)
+         , 1
+         , ifelse((!is.na(a) & a == 2) | (!is.na(b) & b == 2)
+             , 2
+             , NA
+             )
+         )
> cbind(a, b, c1)
a  b c1
[1,]  2 NA  2
[2,] NA  1  1
[3,] NA  1  1
[4,] NA NA NA
[5,]  2  2  2
[6,]  2  2  2
[7,] NA  2  2
[8,]  2  2  2
[9,] NA  2  2
[10,]  2  2  2
>

On Fri, Apr 8, 2011 at 1:56 PM, wgu <wgu at uab.edu> wrote:
> I have used R for years but run into a seemingly simple problem involving 'ifelse'.  condensed code like this
>
>  a=c(2,NA,NA,NA,2,2,NA,2,NA,2)
>  b=c(NA,1,1,NA,2,2,2,2,2,2)
>
> #I want to combined a and b into c so that c would be a valid number either a or b is not missing
>
> c=ifelse(a==1|b==1,1,ifelse(a==2|b==2,2,NA))
> cbind(a,b,c)
>
>          a  b  c
>  [1,]  2 NA NA
>  [2,] NA  1  1
>  [3,] NA  1  1
>  [4,] NA NA NA
>  [5,]  2  2  2
>  [6,]  2  2  2
>  [7,] NA  2 NA
>  [8,]  2  2  2
>  [9,] NA  2 NA
> [10,]  2  2  2
>
> look at rows 1, 7 and 9, c supposes to be 2 but got NA instead. seemingly, the second 'ifelse' doesn't perform as it supposes.
>
> my R version is 2.12.2
>
> any suggestion
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> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?

```