Re: [R] Reorder data frame columns by negating list of names

From: Barry Rowlingson <b.rowlingson_at_lancaster.ac.uk>
Date: Tue, 12 Feb 2008 17:44:37 +0000

Thompson, David (MNR) wrote:
> Hello,
>
> I would like to reorder columns in a data frame by their names as
> demonstrated below:
>
> Take this data frame:
> > xxx <- data.frame(matrix(1:40, ncol=8))
> > names(xxx) <- letters[1:8]
> > xxx
> a b c d e f g h
> 1 1 6 11 16 21 26 31 36
> 2 2 7 12 17 22 27 32 37
> 3 3 8 13 18 23 28 33 38
> 4 4 9 14 19 24 29 34 39
> 5 5 10 15 20 25 30 35 40
>
> and reorder the columns like this:
> > xxx[,c( c('b', 'd', 'h'), c('a', 'c', 'e', 'f', 'g') )]
> b d h a c e f g
> 1 6 16 36 1 11 21 26 31
> 2 7 17 37 2 12 22 27 32
> 3 8 18 38 3 13 23 28 33
> 4 9 19 39 4 14 24 29 34
> 5 10 20 40 5 15 25 30 35
>
> where I only have to name the columns that I'm interested in moving to
> the first few positions, something like:
> > xxx[,c( c('b', 'd', 'h'), -c('b', 'd', 'h') )]
> Error in -c("b", "d", "h") : invalid argument to unary operator
>
> Suggestions? and Thank you, DaveT.

With:

 > move
[1] "b" "d" "h"

  you can do:

 > xxx[,c(match(move,names(xxx)),(1:dim(xxx)[2])[-match(move,names(xxx))])]

    b d h a c e f g
1 6 16 36 1 11 21 26 31
2 7 17 37 2 12 22 27 32
3 8 18 38 3 13 23 28 33
4 9 19 39 4 14 24 29 34
5 10 20 40 5 15 25 30 35

  It basically uses match() to convert names to column numbers. You cant mix positive and negative indices so you need to take the matches you've got away from the 1:dim(xxx)[2] and that gives you the leftover column numbers.

  Don't forget to add a comment.

Barry



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