[R] simple data.frame question

[David Winsemius]

On May 16, 2012, at 11:56 AM, Troels Ring wrote:

> Dear friends - I hope you will forgive me another simple question,  
> illustrated by
>
> ID <- c(1,1,1,2,2,3,3,3)
> PERIOD <- c(1,2,3,2,3,1,2,3)
> X <- runif(8,0,10))

Extraneous paren removed:

>
> FF <- data.frame(ID=ID,PERIOD=PERIOD,X=X)
>
> I need to the fourth value of X as NA, and ID and PERIOD is updated  
> to 1,1,1,2,2,2,3,3,3 and 1,2,3,1,2,3,1,2,3 respectively.
> How do I use the pattern in ID and PERIOD to find the lacking X and  
> put NA?

 > ffnew=merge(x=expand.grid(1:3,1:3),
+ y=FF, by =1:2, all.x=TRUE)
 > ffnew
   Var1 Var2         X
1    1    1 6.6294571
2    1    2 0.5749111
3    1    3 8.7895630
4    2    1        NA
5    2    2 5.7213062
6    2    3 6.1030507
7    3    1 8.9182841
8    3    2 4.2823937
9    3    3 8.8249263
>
> Best wishes
>
> Troels Ring,
> Aalborg, Denmark
>
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David Winsemius, MD
West Hartford, CT