[R] sort rows of matrix by rows of another matrix

[markleeds at verizon.net]

below is another way ( maybe the same ?  )but with an extra line to make 
roworder. i'm also not clear on why I  have to take the transpose of 
the result that
comes back form the apply call. in ?apply, it says that the function 
tries to convert the result back to a matrix. that's fine but why does 
it do
it in the opposite way from the way the data in sent in ( i.e : by row 
). if someone could explain that, i'd appreciate it.


a1 <- structure(c(7, 4, 4, 0, 6, 2, 7, 3, 8, 4, 2, 8), .Dim = c(4L, 3L))
a2 <- structure(c(101L, 101L, 101L, 101L, 102L, 102L, 102L, 102L, 103L,
103L, 103L, 103L), .Dim = c(4L, 3L))

roworder <- t(apply(a1,1,order))

a3 <- t(sapply(1:nrow(a2),function(.rowind) {
   a2[.rowind,roworder[.rowind,]]
}))

print(a3)



On Thu, Jul 31, 2008 at  6:05 PM, Johnson, Eric A. (Seattle) wrote:

> If you're not adverse to cbind-ing a1 and a2, you can use this:
>
> a1a2 <- cbind(a1, a2)
>
> a3 <- t(apply(a1a2, 1, function(x) x[order(x[1:ncol(a1)])+ncol(a1)]))
>
> Eric
>
>
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org]
> On Behalf Of Timothy W. Hilton
> Sent: Thursday, July 31, 2008 2:19 PM
> To: r-help at r-project.org
> Subject: [R] sort rows of matrix by rows of another matrix
>
> Hello all,
>
> I am trying to sort rows of one matrix by rows of another.  Given a1 
> and
> a2:
>
> ------
>> a1
>      [,1] [,2] [,3]
> [1,]    7    6    8
> [2,]    4    2    4
> [3,]    4    7    2
> [4,]    0    3    8
>
> a1 <-
> structure(c(7, 4, 4, 0, 6, 2, 7, 3, 8, 4, 2, 8), .Dim = c(4L, 3L))
>
>> a2
>      [,1] [,2] [,3]
> [1,]  101  102  103
> [2,]  101  102  103
> [3,]  101  102  103
> [4,]  101  102  103
>
> a2 <-
> structure(c(101L, 101L, 101L, 101L, 102L, 102L, 102L, 102L, 103L, 
> 103L, 103L, 103L), .Dim = c(4L, 3L))
> ------
>
> I want to get a3:
>
>> a3
>      [,1] [,2] [,3]
> [1,]  102  101  103
> [2,]  102  101  103
> [3,]  103  101  102
> [4,]  101  102  103
>
> where the rows of a3 are the rows of a2 sorted according to the rows 
> of
> a1.
>
> I can get the necessary sorting index:
>> apply(a1, 1, order)
>      [,1] [,2] [,3] [,4]
> [1,]    2    2    3    1
> [2,]    1    1    1    2
> [3,]    3    3    2    3
>
> and I can get the rows of a1 sorted according to the rows of a1:
>> t(apply(a1, 1, function(x) x[order(x)]))
>      [,1] [,2] [,3]
> [1,]    6    7    8
> [2,]    2    4    4
> [3,]    2    4    7
> [4,]    0    3    8
>
> but I can't get the rows of a2 sorted according to the rows of a1...
>
> Thanks,
> Tim
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.