R help - May 2009 - Sort matrix by column 1 ascending then by column 2 decending

I've got a matrix with 2 columns and n rows. I need to sort it first
by the values in column 1 ascending. Then for values which are the
same in column 1, sort by column 2 decending. For example:

2 .5
1 .3
1 .5
3 .2

Goes to:

1 .5
1 .3
2 .5
3 .2

This is easy to do in spreadsheet programs but I can't seem to work
out how to do it in R and haven't been able to find a solution
anywhere.


Thanks!

-Paul.

-- 
Paul Geeleher
School of Mathematics, Statistics and Applied Mathematics
National University of Ireland
Galway
Ireland

Try this:

cbind(sort(x[,1]), unlist(tapply(x[,2], x[,1], sort, decreasing = T)))

On Wed, May 27, 2009 at 9:39 AM, Paul Geeleher
<paulgeeleher@gmail.com>wrote:
> I've got a matrix with 2 columns and n rows. I need to sort it first
> by the values in column 1 ascending. Then for values which are the
> same in column 1, sort by column 2 decending. For example:
>
> 2 .5
> 1 .3
> 1 .5
> 3 .2
>
> Goes to:
>
> 1 .5
> 1 .3
> 2 .5
> 3 .2
>
> This is easy to do in spreadsheet programs but I can't seem to work
> out how to do it in R and haven't been able to find a solution
> anywhere.
>
>
> Thanks!
>
> -Paul.
>
> --
> Paul Geeleher
> School of Mathematics, Statistics and Applied Mathematics
> National University of Ireland
> Galway
> Ireland
>
> ______________________________________________
> R-help@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.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

It's a very interesting problem. I just wrote a function for it:

order.matrix <- function(m, columnsDecreasing = c('1'=FALSE), rows =
1:nrow(m))
{
  if (length(columnsDecreasing) > 0)
  {
    col <- as.integer(names(columnsDecreasing[1]));
    values <- sort(unique(m[rows, col]), decreasing=columnsDecreasing[1]);
    unlist(sapply(values, function(x) order.matrix(m,
columnsDecreasing[-1], which((1:nrow(m) %in% rows) & (m[,
col]==x)))));
  }
  else
  {
    rows;
  }
}

For instance:
> m <- matrix( c(2, 1, 1, 3, .5, .3, .5, .2), 4)
> m
     [,1] [,2]
[1,]    2  0.5
[2,]    1  0.3
[3,]    1  0.5
[4,]    3  0.2
> m[order.matrix(m),]
     [,1] [,2]
[1,]    1  0.3
[2,]    1  0.5
[3,]    2  0.5
[4,]    3  0.2
> m[order.matrix(m, c("1"=FALSE, "2"=TRUE)),]
     [,1] [,2]
[1,]    1  0.5
[2,]    1  0.3
[3,]    2  0.5
[4,]    3  0.2

Any comment is welcome! ;)

On Wed, May 27, 2009 at 11:04 PM, Linlin Yan <yanlinlin82 at gmail.com>
wrote:
>> m <- matrix( c(2, 1, 1, 3, .5, .3, .5, .2), 4)
>> m
> ? ? [,1] [,2]
> [1,] ? ?2 ?0.5
> [2,] ? ?1 ?0.3
> [3,] ? ?1 ?0.5
> [4,] ? ?3 ?0.2
>> m[unlist(sapply(sort(unique(m[,1])), function(x)
which(m[,1]==x)[order(m[(m[,1]==x),2], decreasing=TRUE)])),]
> ? ? [,1] [,2]
> [1,] ? ?1 ?0.5
> [2,] ? ?1 ?0.3
> [3,] ? ?2 ?0.5
> [4,] ? ?3 ?0.2
>
> On Wed, May 27, 2009 at 8:39 PM, Paul Geeleher <paulgeeleher at
gmail.com> wrote:
>> I've got a matrix with 2 columns and n rows. I need to sort it
first
>> by the values in column 1 ascending. Then for values which are the
>> same in column 1, sort by column 2 decending. For example:
>>
>> 2 .5
>> 1 .3
>> 1 .5
>> 3 .2
>>
>> Goes to:
>>
>> 1 .5
>> 1 .3
>> 2 .5
>> 3 .2
>>
>> This is easy to do in spreadsheet programs but I can't seem to work
>> out how to do it in R and haven't been able to find a solution
>> anywhere.
>>
>>
>> Thanks!
>>
>> -Paul.
>>
>> --
>> Paul Geeleher
>> School of Mathematics, Statistics and Applied Mathematics
>> National University of Ireland
>> Galway
>> Ireland
>>
>> ______________________________________________
>> 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.
>>
>

On 5/27/2009 8:39 AM, Paul Geeleher wrote:
> I've got a matrix with 2 columns and n rows. I need to sort it first
> by the values in column 1 ascending. Then for values which are the
> same in column 1, sort by column 2 decending. For example:
You've seen a few ways.  Here are some more:

1.  Use the fact that order() uses a stable sort algorithm, so just sort 
by the second column then the first:

x <- matrix(c(2,1,1,3,.5,.3,.5,.2), ncol=2)
x1 <- x[order(x[,2], decreasing=TRUE),]
x2 <- x1[order(x1[,1]),]
x2

2.  Use the fact that your values are numeric, so negatives sort in the 
reverse order of positives:

x[order(x[,1], -x[,2]),]

3.  If the values aren't known to be numeric, convert them to numeric 
before using them as sort keys:

x[order(xtfrm(x[,1]), -xtfrm(x[,2])),]

In any of these, watch out for NA handling.  My methods all put NA 
values last, but that might not be what you want.

Duncan Murdoch
> 
> 2 .5
> 1 .3
> 1 .5
> 3 .2
> 
> Goes to:
> 
> 1 .5
> 1 .3
> 2 .5
> 3 .2
> 
> This is easy to do in spreadsheet programs but I can't seem to work
> out how to do it in R and haven't been able to find a solution
> anywhere.
> 
> 
> Thanks!
> 
> -Paul.
>