R help - May 2011 - Order a matrix

Dear all,

I just want to order a matrix using several columns in a matrix. For
example:

x <- matrix(sample(c(1:5), 60, replace = T), 10, 6).

If I order the matrix by the first two columns, I will do it like this:
 
x[order(x[, 1], x[, 2]), ]. 

But when I repeat this work many times and the columns will change each time
in a simulation study, how can I assign the arguments of order()? For
example, in the first iteration, the columns needing to order is the first
two columns, in the second iteration, the columns needing to order is the
first, second, and fourth column? ?.

I would appreciate any help on this question. Thanks a lot.

Lisa


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Try using do.call("order", listOfColumnsToSortBy), as in
  cols <- c(1,3,4)
  x[do.call("order", as.data.frame(x[,cols])), ]

To be really safe you should remove the names from the data.frame
produced by as.data.frame (in case they match the argument names
of order), as in
  x[do.call("order", unname(as.list(as.data.frame(x[,cols])))),]
or
  x[do.call("order", unname(split(x[,cols], col(x[,cols])))), ]

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 Lisa
> Sent: Tuesday, May 24, 2011 12:00 PM
> To: r-help at r-project.org
> Subject: [R] Order a matrix
> 
> Dear all,
> 
> I just want to order a matrix using several columns in a matrix. For
> example:
> 
> x <- matrix(sample(c(1:5), 60, replace = T), 10, 6).
> 
> If I order the matrix by the first two columns, I will do it 
> like this:
>  
> x[order(x[, 1], x[, 2]), ]. 
> 
> But when I repeat this work many times and the columns will 
> change each time
> in a simulation study, how can I assign the arguments of order()? For
> example, in the first iteration, the columns needing to order 
> is the first
> two columns, in the second iteration, the columns needing to 
> order is the
> first, second, and fourth column? ....
> 
> I would appreciate any help on this question. Thanks a lot.
> 
> Lisa
> 
> 
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> View this message in context: 
> http://r.789695.n4.nabble.com/Order-a-matrix-tp3547923p3547923.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Hi, Bill,

Thank you for your help. Your R script works very well. 

Lisa

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