[R] Ordering a matrix by row value in R2.15

[Pete Brecknock]

fitz_ra wrote
> I know this is posted a lot, I've been through about 40 messages reading
> how to do this so let me apologize in advance because I can't get this
> operation to work unlike the many examples shown.
> 
> I have a 2 row matrix 
>> temp
>        [,1]     [,2]     [,3]     [,4]     [,5]     [,6]     [,7]     [,8]    
> [,9]    [,10]
> [1,] 17.000 9.000000 26.00000  5.00000 23.00000 21.00000 19.00000 17.00000
> 10.00000  63.0000
> [2,] 15.554 7.793718 33.29079 15.53094 20.44825 14.34443 11.83552 11.62997
> 10.16019 115.2602
> 
> I want to order the matrix using the second row in ascending order.  From
> the many examples (usually applied to columns) the typical solution
> appears to be: 
>> temp[order(temp[2,]),]
> Error: subscript out of bounds
> 
> However as you can see I get an error here.
> 
> When I run this one line command:
>> sort(temp[2,])
>  [1]   7.793718  10.160190  11.629973  11.835520  14.344426  15.530939 
> 15.553999  20.448249  33.290789
> [10] 115.260192
> 
> This works but I want the matrix to update and the corresponding values of
> row 1 to switch with the sort.

Maybe consider the order function ....

orig <- matrix(c(10,20,30,3,1,2), nrow=2, byrow=TRUE)

new <-t(apply(orig,1,function(x) x[order(orig[2,])]))

> orig
     [,1] [,2] [,3]
[1,]   10   20   30
[2,]    3    1    2
> new
     [,1] [,2] [,3]
[1,]   20   30   10
[2,]    1    2    3

HTH 

Pete




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