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

[William Dunlap]

fitz_ra <no address>
> > 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

That tries to reorder the rows of temp according the values in its second
row, which causes the error (unless you are unlucky and have more rows than
columns, in which case you silently get a wrong answer).  You want to reorder
the columns of temp, so make the output of order() the column (second)
argument to [,]:

  > temp[, order(temp[2,])]
           [,1]     [,2]     [,3]     [,4]     [,5]     [,6]   [,7]     [,8]
  [1,] 9.000000 10.00000 17.00000 19.00000 21.00000  5.00000 17.000 23.00000
  [2,] 7.793718 10.16019 11.62997 11.83552 14.34443 15.53094 15.554 20.44825
           [,9]    [,10]
  [1,] 26.00000  63.0000
  [2,] 33.29079 115.2602

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Pete Brecknock
> Sent: Sunday, March 24, 2013 5:12 PM
> To: r-help at r-project.org
> Subject: Re: [R] Ordering a matrix by row value in R2.15
> 
> 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
> 
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Ordering-a-matrix-by-row-
> value-in-R2-15-tp4662337p4662340.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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