Feature Request: Allow fct_reorder to Work with Non-Numeric Results of .fun

[billdenney]

This is the same issue as #103 with a different request.

It seems as though fct_reorder() and fct_reorder2() should only require that the results of the function are sortable not that they are numeric. Lexicographical order for the below is consistent and well-defined, but a simple numerical mapping can be more complex when the input isn't as simple as the below.

My feature request is: Can fct_reorder() and fct_reorder2() please allow non-numeric values? It seems like it could be as simple as running xtfrm() on the results of .fun.

Related to this, can the documentation be updated to indicate what the return value of .fun() must be?

library(forcats)
fct_reorder(.f=LETTERS[1:3], .x=LETTERS[4:6], .fun=min)
#> Error: `fun` must return a single number per group

Created on 2018-09-11 by the reprex package (v0.2.0).

[hadley]

Seems reasonable to me.

[alexkgold]

Going to work on this for tidyverse dev day!

[billdenney]

@akgold, I generated a PR for this several days ago (but it didn't link because I misunderstood how automatic linking between PR and issues worked-- titles don't link). Linked now.

[alexkgold]

@billdenney Ah, cool! Nevermind :)