[R] look up and Missing

[David Winsemius]

On Nov 8, 2009, at 11:08 AM, David Winsemius wrote:

>
> 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))

A further thought, that might be more useful if you were intending to  
supply a portion of a dataframe to an analytical function, would be  
the subset function:

t2 <- subset(temp, v2 != -9)

E. g.:

lm( v1 ~ v2 + v3, data= subset(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
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT