stri_order - multiple keys

[gagolews]

allow stri_order(list(x, y, z))

However, a common use case would be mixed-type inputs (e.g., a data frame columns): numeric, character, factor, etc.; coercion of such inputs to character [as usual in stringi] might not be the best idea..

[gagolews]

stri_sort_key() could be used for this purpose + pass the converted data (character only? don't convert factors to strings?) to the base order(0).

Update: stri_sort_key returns bytes-encoded strings, order does not accept them. Moreover, order must've been called with C/POSIX locale set.

To do: introduce stri_rank

[gagolews]

Sorting wrt 2+ arguments can be performed, for example, like:

> x <- ToothGrowth[sample(nrow(ToothGrowth), 10), ]
> x[order(stri_rank(x$supp), x$len), ]
    len supp dose
35 14.5   OJ  0.5
41 19.7   OJ  1.0
54 24.5   OJ  2.0
52 26.4   OJ  2.0
44 26.4   OJ  1.0
10  7.0   VC  0.5
18 14.5   VC  1.0
14 17.3   VC  1.0
19 18.8   VC  1.0
24 25.5   VC  2.0
> x[order(-stri_rank(x$supp), x$len), ]
    len supp dose
10  7.0   VC  0.5
18 14.5   VC  1.0
14 17.3   VC  1.0
19 18.8   VC  1.0
24 25.5   VC  2.0
35 14.5   OJ  0.5
41 19.7   OJ  1.0
54 24.5   OJ  2.0
52 26.4   OJ  2.0
44 26.4   OJ  1.0


> X <- data.frame(a=c("b", NA, "b", "b", NA, "a", "a", "c"), b=runif(8))
> X[order(stri_rank(X$a), X$b), ]
     a          b
7    a 0.01393522
6    a 0.70113965
4    b 0.08760199
1    b 0.28077931
3    b 0.70474734
8    c 0.73574582
5 <NA> 0.22125663
2 <NA> 0.95334338

Because of this, I don't think we need another function.
I will include a relevant example in the manual.