Dart - Split String by RegEx

Question

I am trying to split a string like this:

x^-5 - 3

into a list like this:

[x^-5, -, 3]

The first minus after the ^ must be at the same list index as the x, because it's just the negative exponent. However, I want other minuses, which are not an exponent of anything, to be on their own index.

When splitting by -, obviously my x^-5 gets split into two as well.

So is there any way I can achieve this using RegEx or something like that?

Thanks in advance

Did you try splitting with whitespace? .split(new RegExp(r"\s+")) — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Apr 26, 2017 at 11:43
Sorry, I forgot to mention that it should work without whitespace... But If I don't find another solution, I'll stick to whitespace, thanks. — OhMad
– OhMad, Commented Apr 26, 2017 at 11:50
It turns out, in Dart, you cannot use a JS approach to capture subpatterns to return with the split chunks. You'd better write a parser or use any ready-made libraries. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Apr 26, 2017 at 11:56

Community · Accepted Answer · 2017-05-23 12:26:01Z

8

If you use allMatches instead of split, you can use a pattern like this:

(?:\^\s*-|[^\-])+|-

Working example: DartPad

We match tokens that consist of anything except -, or ^-.
If we reach a - that is not an exponent, we match it alone, similar to a split.

Some notes:

There are similar patterns, this may not be the most efficient, but it is short.
If you are matching mathematical expressions, there are many things that can go wrong (for example parentheses), regular expressions are not a good way to achieve that.
This is basically the match to skip trick.

edited May 23, 2017 at 12:26

CommunityBot

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answered Apr 26, 2017 at 12:25

Kobi

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6 Comments

Kobi Over a year ago

In other languages you could've used a lookbehind, (?<!\^)-, but that isn't supported on JavaScript (and Dart).

OhMad Over a year ago

Wow, awesome. Exactly what I was looking for, thank you :)

OhMad Over a year ago

Btw what would you use instead of regex?

Kobi Over a year ago

@Rechunk - For example, in JavaScript, I found a library called Math.js, that can parse expressions: mathjs.org/docs/expressions/parsing.html#parse . For Dart, there's this: Is there a math parser for petitparser?, and math_expressions (beta)

OhMad Over a year ago

how would I extend this regex to be able to split something like this: x^-5 + 3 (with a plus) into this: [x^-5, +, 3]?

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