R help - Jul 2011 - replacing elements of vector through elements of another vector

Hello everybody,

I hope this question is not too silly but I'm almost going crazy about
that and could not find a solution.

I have two variables, say A and B and I would like to combine them in C.
In particular I want a C-value of B when B is not NA and the A value in
case that B is NA:

A   B   C
2   NA  2
3   4   4
NA  3   3
4   1   1
2   NA  2
1   4   4
NA  NA  NA
5   3   3
4   1   1

I tried something like:

C <- B #assigning variable B to variable C
C[is.na(B) & A >= 0] <- A #using value of A in case that B is na

but this results in an error message about the unequal length of the
replacement and what has to be replaced...

I guess I am too deep in the problem to see the (probably) easy
solution, hence any hints and advices are appreciated.

Thank you very much!

Marcus
-- 
Dipl.-Psych. Marcus Mund
Friedrich-Schiller-University Jena
Institute for Psychology
Department of Personality Psychology and Psychological Assessment
Humboldtstra?e 11/Raum 111
07743 Jena, Germany

Tel.: +49 3641/9-45 960
Mail: marcus.mund at uni-jena.de
Fingerprint: 6B15F90EA7752D9E327A055427F4F5DC255188C4

On Jul 27, 2011, at 9:52 AM, Marcus Mund wrote:
> Hello everybody,
> 
> I hope this question is not too silly but I'm almost going crazy about
> that and could not find a solution.
> 
> I have two variables, say A and B and I would like to combine them in C.
> In particular I want a C-value of B when B is not NA and the A value in
> case that B is NA:
> 
> A   B   C
> 2   NA  2
> 3   4   4
> NA  3   3
> 4   1   1
> 2   NA  2
> 1   4   4
> NA  NA  NA
> 5   3   3
> 4   1   1
> 
> I tried something like:
> 
> C <- B #assigning variable B to variable C
> C[is.na(B) & A >= 0] <- A #using value of A in case that B is na
> 
> but this results in an error message about the unequal length of the
> replacement and what has to be replaced...
> 
> I guess I am too deep in the problem to see the (probably) easy
> solution, hence any hints and advices are appreciated.
> 
> Thank you very much!
> 
> Marcus


Something like this:
> DF
   A  B
1  2 NA
2  3  4
3 NA  3
4  4  1
5  2 NA
6  1  4
7 NA NA
8  5  3
9  4  1

> with(DF, ifelse(!is.na(B), B, A))
[1]  2  4  3  1  2  4 NA  3  1


HTH,

Marc Schwartz

On Jul 27, 2011, at 10:52 AM, Marcus Mund wrote:
> Hello everybody,
>
> I hope this question is not too silly but I'm almost going crazy about
> that and could not find a solution.
>
> I have two variables, say A and B and I would like to combine them  
> in C.
> In particular I want a C-value of B when B is not NA and the A value  
> in
> case that B is NA:
>
> A   B   C
> 2   NA  2
> 3   4   4
> NA  3   3
> 4   1   1
> 2   NA  2
> 1   4   4
> NA  NA  NA
> 5   3   3
> 4   1   1
>
> I tried something like:
>
> C <- B #assigning variable B to variable C
> C[is.na(B) & A >= 0] <- A #using value of A in case that B is na
Just use:

  C[is.na(B) ] <- A[is.na(B) ]

# doesn't matter what A is. Or if it does, then use same logical vecot  
index on both sides

You need to have is.na(B) on both sides to get the vector assignments  
to match up. That is what the error message is telling you.
>
> but this results in an error message about the unequal length of the
> replacement and what has to be replaced...
>
> I guess I am too deep in the problem to see the (probably) easy
> solution, hence any hints and advices are appreciated.
>
> Thank you very much!
>
> Marcus
> -- 
> Dipl.-Psych. Marcus Mund
> Friedrich-Schiller-University Jena
> Institute for Psychology
> Department of Personality Psychology and Psychological Assessment
> Humboldtstra?e 11/Raum 111
> 07743 Jena, Germany
>
> Tel.: +49 3641/9-45 960
> Mail: marcus.mund at uni-jena.de
> Fingerprint: 6B15F90EA7752D9E327A055427F4F5DC255188C4
>
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