[R] same value in column-->delete

[jim holtman]

Try this:

> x
  id snp1 snp2 snp3
1  1    A    G    G
2  2    G    G    G
3  3    G    G    A
> str(x)
'data.frame':   3 obs. of  4 variables:
 $ id  : num  1 2 3
 $ snp1: Factor w/ 2 levels "A","G": 1 2 2
 $ snp2: Factor w/ 1 level "G": 1 1 1
 $ snp3: Factor w/ 2 levels "A","G": 2 2 1
> # test for which columns are the same
> apply(x, 2, function(.col) all(head(.col, -1) == tail(.col, -1)))
   id  snp1  snp2  snp3
FALSE FALSE  TRUE FALSE
>


On Thu, Mar 26, 2009 at 7:15 AM, Duijvesteijn, Naomi
<Naomi.Duijvesteijn at ipg.nl> wrote:
>
>   Hi Readers,
>
>
>   I have a question.
>
>
>   I have a large dataset and want to throw away columns that have the same
>   value in the column itself and I want to know which column this was.
>
>
>   For example
>
>   > x<-data.frame(id=c(1,2,3), snp1=c("A","G",
>   "G"),snp2=c("G","G","G"),snp3=c("G","G","A"))
>
>   > x
>
>     id snp1 snp2 snp3
>
>   1  1    A    G    G
>
>   2  2    G    G    G
>
>   3  3    G    G    A
>
>
>   Now I want to know that snp2 in monomorphic (the same value for the column)
>   and after I know which column it is I want to take these columns out.
>
>
>   Thanks,
>
>   Naomi
>
>
>
>
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?