same value in column-->delete

this works

which.is.not.unique <- apply(x,2,function(x)ifelse(length(unique(x))==1,F,T))
x[,which.is.not.unique]

patrizio

2009/3/26 Duijvesteijn, Naomi <Naomi.Duijvesteijn at ipg.nl>:

  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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