Convert full-width Japanese text to half-width (zen-kaku to han-kaku)

Question

In PHP it's possible to convert double-width characters to single width with the function mb_convert_kana. They call it "convert zen-kaku to han-kaku". For example, I have a string to convert:

dbl = "ＢＯＸ"

and I'd like to find some method like this

dbl = "ＢＯＸ".convert_to_half_width # dbl is now "BOX"

Is there a way to do this in Ruby?

Answer 1

I use a combination of the Ruby built-in NKF and String#tr

require 'nkf'
dbl = "ＢＯＸｶﾀｶﾅ"
dbl = NKF.nkf('-X -w', dbl).tr('０-９ａ-ｚＡ-Ｚ', '0-9a-zA-Z')
# dbl now is "BOXカタカナ"

This has the added benefit of transposing half-width katakana to full-with katakana as well.