[R] look up and Missing

[David Winsemius]

On Nov 8, 2009, at 10:23 AM, Ashta wrote:

> HI  R-Users
>
> Assume that I have a data frame 'temp' with several variables  
> (v1,v2,v3,v4,v5.).
>
>  v1 v2 v3  v4 v5
>   1  2   3   3    6
>   5  2  4    2    0
>   2 -9   5   4    3
>   6  2   1   3    4
>
> 1, I want to look at the entire row values of when v2 =-9
>   like
>         2 -9   5   4    3


> I wrote
> K<- list(if(temp$v2)==-9))

"if" would be the wrong R function to use. It's mostly for program  
control. And where did the "3" come from? You were working with the  
column temp$v2. Oh, you wanted a row rather than the column, "v2"? So  
how were you going to select that row? Perhaps:

K <-temp[ temp$v2 == -9, ]
K

>
> I wrote the like this but  it gave me  which is not correct.
>   False false false false false

I could not get your code to produce this. I got:
Error: unexpected '==' in "K<- list(if(temp$v2)=="

>
> 2. I want assign that values  as missing if   v2 = -9.  (ie., I want
> exclude from the analysis
>
> How do I do it  in R?

Your request is not well specified at least to my reading, because I  
could not tell if you wanted the re-assignment to occur in temp (and  
that was after I came down on the row side of the whether you wanted a  
row or column.) . The following assumes you wanted the row in question  
(created above)  modified outside of "temp".

 > is.na(K) <- K == -9
 > K
   v1 v2 v3 v4 v5
3  2 NA  5  4  3

If you had used ifelse you would have gotten close, but the data type  
would have been a list, which may not have been what you expected:

 > K <- ifelse(K==-9, NA, K)
 > K
[[1]]
[1] 2

[[2]]
[1] NA

[[3]]
[1] 5

[[4]]
[1] 4

[[5]]
[1] 3

>
-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT