MatthewMDavis
String.split on a sub-string within a pattern?
I’m trying all sorts of things with no luck, so I thought I’d ask for some help.
I want to split a string anytime there’s a “b” in “abc”, but not in " b ". I.e., when a “b” is surrounded by whitespace, I don’t want it to be a splitting character, but an element in the array returned by the split.
String.split("abcde", regex) == ["a", "cde"]
String.split("a b cde", regex) == ["a", "b", "cde"]
So I need (I think) a way to craft a regex that looks for abc, but only splits on the b part.
Marked As Solved
jwarlander
Regex Negative Lookbehind is your friend in cases like this:
iex(24)> String.split("abcde", ~r/((?<!\s)b(?!\s)|\s)/)
["a", "cde"]
iex(25)> String.split("a b cde", ~r/((?<!\s)b(?!\s)|\s)/)
["a", "b", "cde"]
iex(26)> String.split("ab cde", ~r/((?<!\s)b(?!\s)|\s)/)
["ab", "cde"]
iex(27)> String.split("a bcde", ~r/((?<!\s)b(?!\s)|\s)/)
["a", "bcde"]
The above pattern will match a b for splitting, only if it’s entirely surrounded by non-whitespace, eg. it’s not preceded by whitespace ((?<!\s)) and it’s not followed by whitespace ((?!\s)). It’ll also split on standalone whitespace ((...|\s)).
Depending on your exact needs you may want to adjust the pattern, of course.
Also Liked
JEG2
I think the pattern can be even simpler. Can you show some sample inputs and what you want to see as outputs?
swelham
I read this blog series(sorry it’s in python) last year that I think will help. It’s about building a simple interpreter and it starts off with simple maths and then onto supporting order of operation. Also requires no regex 
Last Post!
tallakt
\B matches non word boundary, ie. not at the beginning of a word
iex(9)> for s <- ["abcde", "a b cde"], do: String.split(s, ~r(\Bb|\s))
[["a", "cde"], ["a", "b", "cde"]]
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