[Rd] Suggestion: Help users sort data frames

Gabor Grothendieck ggrothendieck at gmail.com
Sat Jul 9 02:06:19 CEST 2005

This functionality does seem needed in base R to me too but
in the interim you could create a package to make it available on 
CRAN or if that seems excessive for just one function you could 
contact the author of one of the multi-author packages and see if 
they would include it in their package.  

On 7/8/05, kwright at eskimo.com <kwright at eskimo.com> wrote:
> I've noticed that a frequently asked question on R-help is how to sort a
> data frame by multiple columns.  Since this question is asked so often,
> making this task easier for users seems a worthwhile goal.
> At a minimum, the following changes to the documentation would surely be
> helpful and reduce email postings to R-help:
> 1. In the "See Also" section of the help page for 'sort' it currently says:
> "order for sorting on or reordering multiple variables".
> Appending the phrase "(including data frames)" could be helpful.
> 2. Include a simple example on sorting a data frame in the 'sort' help.
> In an ideal world this example should belong in the help for 'order', but
> people are going to be reading the 'sort' page first.  Here's one example:
> # Sort a data frame by multiple columns
> d = data.frame(b=factor(c("Hi","Med","Hi","Low"),levels=c("Low","Med","Hi"),
>               ordered=TRUE),
>               x=c("A","D","A","C"),y=c(8,3,9,9),z=c(1,1,1,2))
> d[order(d$b,d$z,d$y),]
> 3. It looks like the help page for 'order' only shows sorting of matrices
> (and row-wise sorting at that!).  Since column-wise sorting is may be more
> common, the example above might beneficially be included in the 'order'
> help page as well.
> A minor bug-report here: The help for 'order' includes this example:
>  ## For character vectors we can make use of rank:
>  cy <- as.character(y)
>  rbind(x,y,z)[, order(x, -rank(y), z)]
> I'm not sure what the intention was, but 'cy' is not used, so something
> seems to be amis.
> Alternatively, I wrote a formula-based function for sorting data frames
> via calls like: sort.data.frame(~ -x +y +z, dat)
> The function can be found here:
>  http://tolstoy.newcastle.edu.au/R/help/04/09/4300.html
> When emails to R-help ask how to sort data frames, responses often
> reference this function so it seems to have been very helpful for people.
> I showed the function to Thomas Lumley and he said it looked nice but that
> using a minus sign for reverse sorting is a bit anti-R flavored since a
> minus sign usually means to omit terms from a formula.
> Sincerely,
> Kevin Wright
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