[R] Simple order() data frame question.

[John Kane]

Argh.  I knew it was at least partly obvious.  I never have been able to read the order() help page and understand what it is saying.

THanks very much.

By the way, to me it is counter-intuitive that the the command is

> df1[order(df1[,2],decreasing=TRUE),]

For some reason I keep expecting it to be 
order( , df1[,2],decreasing=TRUE)

So clearly I don't understand what is going on but at least I a lot better off.  I may be able to get this graph to work.  



--- On Thu, 5/12/11, Patrick Breheny <patrick.breheny at uky.edu> wrote:

> From: Patrick Breheny <patrick.breheny at uky.edu>
> Subject: Re: [R] Simple order()  data frame question.
> To: "John Kane" <jrkrideau at yahoo.ca>
> Cc: "R R-help" <r-help at stat.math.ethz.ch>
> Received: Thursday, May 12, 2011, 8:44 AM
> On 05/12/2011 08:32 AM, John Kane
> wrote:
> > Clearly, I don't understand what order() is doing and
> as ususl the help for order seems to only confuse me more.
> For some reason I just don't follow the examples there. I
> must be missing something about the data frame sort there
> but what?
> >
> > I originally wanted to  reverse-order my data
> frame df1 (see below) by aa (a factor) but since this was
> not working I decided to simplify and order by bb to see
> what was haqppening!!
> >
> > I'm obviously doing something stupid but what?
> >
> > (df1<- data.frame(aa=letters[1:10],
> >       bb=rnorm(10)))
> > # Order in acending order by bb
> > (df1[order(df1[,2]),] ) # seems to work fine
> >
> > # Order in decending order by bb.
> > (df1[order(df1[,-2]),])  # does not seem to work
> >
> 
> There is a 'decreasing' option described in the help file
> for 'order' 
> which does what you want:
> 
> df1<- data.frame(aa=letters[1:10],bb=rnorm(10))
> df1[order(df1[,2],decreasing=TRUE),]
> 
>     aa          bb
> 6   f  3.16449690
> 7   g  2.44362935
> 8   h  0.80990322
> 1   a  0.06365513
> 5   e -0.33932586
> 9   i -0.52119533
> 2   b -0.65623164
> 4   d -0.86918700
> 3   c -1.86750927
> 10  j -2.21178676
> 
> df1[order(df1[,1],decreasing=TRUE),]
> 
>     aa          bb
> 10  j -2.21178676
> 9   i -0.52119533
> 8   h  0.80990322
> 7   g  2.44362935
> 6   f  3.16449690
> 5   e -0.33932586
> 4   d -0.86918700
> 3   c -1.86750927
> 2   b -0.65623164
> 1   a  0.06365513
> 
> The expression 'df1[,-2]' removes the second column from
> df1; clearly 
> not what you want here.
> 
> -- 
> Patrick Breheny
> Assistant Professor
> Department of Biostatistics
> Department of Statistics
> University of Kentucky
>