[R] referring to a row number and to a row condition, and to columns simultaneously

[David Winsemius]

On Sep 17, 2009, at 5:17 PM, Dimitri Liakhovitski wrote:

> Hello, dear R-ers!
>
> I have a data frame:
> x<-data.frame(a=c(4,2,4,1,3,4),b=c(1,3,4,1,5,0),c=c(NA, 
> 2,5,3,4,NA),d=rep(NA,6),e=rep(NA,6))
> x
>
> When x$a==1, I would like to replace NAs in columns d and e with 8 and
> 9, respectively
> When x$a != 1, I would like to replace NAs in columns d and e 101 and
> 1022, respectively.
>
> However, I only want to do it for rows 2:5 - while ignoring what's
> happening in rows 1 and 6.
>
> Here is what I've come up with:
>
> x
> for(i in 2:5){
>  x[i & x[[1]]==1,4:5]<-c(8,9)
>  x[i & x[[1]]!=1,4:5]<-c(101,102)
>  }
> x



  x$d[2:5] <- 8*(x$a[2:5] == 1) + 101*(x$a[2:5] != 1)
  x$e[2:5] <- 9*(x$a[2:5] == 1) + 102*(x$a[2:5] != 1)

 > x
   a b  c   d   e
1 4 1 NA  NA  NA
2 2 3  2 101 102
3 4 4  5 101 102
4 1 1  3   8   9
5 3 5  4 101 102
6 4 0 NA  NA  NA


>
> However, something is wrong here.
> First, rows 1 and 6 are not ignored.
> Second, the order of 101 and 102 changes - I, however, always want to
> see 101 in column d and 102 in column e.
>
> Any advice?
> Thanks a lot!
>
> -- 
> Dimitri Liakhovitski
> Ninah.com
> Dimitri.Liakhovitski at ninah.com
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT