How to remove numeric values as character and resort the string accordng unit number

I have this string

 D = c("0" , "11", "12", "13", "14", "15", "16", "21", "22", "23", "24", "25", "26", "31", "32", "33", "34", "35", "36", "41", "42", "43", "44","45", "46","51","52", "53", "54", "55", "56", "61", "62", "63", "64", "65", "66") 

1. If I would to remove those character lower then 30 without transforming the string as numeric, what should I do?

2. If I would like to reorder the string basing on the unit number (meaning that all those with final 1 go before those with final two and so on, such 31, 41, 51, 61, 32, 42 and so on, which should be the opration?

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Thanks

>Solution :

You don’t have to convert to numeric, D[D >= 30] works fine. >= works also for character vectors and the sorting depends then on your locale. Check ?Comparison for more details.

D[D >= "30"]
#[1] "31" "32" "33" "34" "35" "36" "41" "42" "43" "44" "45" "46" "51" "52" "53" "54" "55" "56" "61" "62" "63" "64" "65" "66"

For the sorting, this will work (but probably only if you have 2-digit numbers):

str_rev <- stringi::stri_reverse
str_rev(sort(str_rev(D[D >= "30"])))
# [1] "31" "41" "51" "61" "32" "42" "52" "62" "33" "43" "53" "63" "34" "44" "54" "64" "35"
#[18] "45" "55" "65" "36" "46" "56" "66"

Or with str_sub:

library(stringr)        
D[order(str_sub(D, -1, -1))]