split a mathematical expression on operators and include the operators in the output array

Question

I'm trying to split the mathematical strings on maths operators. for example

expression = "7*6+3/2-5*6+(7-2)*5"

I need to tokenize it to produce:

expressionArray = ["7","*","6","+","3","/","2","-","5","*","6"]

I tried finding the solution here and this is what i get

expressoinArray=expression.split("(?<=[-+*/])|(?=[-+*/]")

but looks like this is not fetching the desired result for expression.

This question makes little sense. The `String` isn't a string, and `String1` is an Array of some, but not all, of the tokens used to assigned to `String`. The value passed to `.split()` is a string sequence of characters seemingly unrelated to anything, though it looks like it could be intended to operate as a regex. And the desired input and output are unclear. — , Jun 11 '13 at 18:32
You say it isn't the desired result, but you also don't say what the desired result is. — Alex W, Jun 11 '13 at 18:45
I think this question is valid and needs to be reopened. One use case for this when converting postfix mathematical notation to prefix using shant yard algorithm. — Mosaaleb, Dec 16 '19 at 00:32

Gabe · Accepted Answer · 2013-06-11T19:05:05.747

8

jsfiddle

var expression = "7.2*6+3/2-5*6+(7-2)*5";
var copy = expression;

expression = expression.replace(/[0-9]+/g, "#").replace(/[\(|\|\.)]/g, "");
var numbers = copy.split(/[^0-9\.]+/);
var operators = expression.split("#").filter(function(n){return n});
var result = [];

for(i = 0; i < numbers.length; i++){
     result.push(numbers[i]);
     if (i < operators.length) result.push(operators[i]);
}

console.log(result);

edited Jun 11 '13 at 19:05

answered Jun 11 '13 at 18:52

Gabe

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The filter method doesn't work in IE 8 or below, just FYI. – Alex W Jun 11 '13 at 18:54
I want to split at operators only, this won't give right result i I have decimal number or more than one digit number. for ex: 7.5*32+2-6.97 – min2bro Jun 11 '13 at 18:56
@min2bro - first off you didn't mention that, second this is all the way there minus changing the regex to get floats. – Gabe Jun 11 '13 at 19:00
@Gabe Thanks much...I'll try some other way to get this done... – min2bro Jun 11 '13 at 19:05
@min2bro - updated to support floats. – Gabe Jun 11 '13 at 19:09
@min2bro - Legends always like upvotes. – Gabe Jun 11 '13 at 19:17
@ I'm yet a novice to upvote legends..Need 9 more reputations to have this privilege to vote.. – min2bro Jun 11 '13 at 19:22
Quality down-vote there, give me a reason. – Gabe Jun 12 '13 at 19:43
1

Note that this answer (and the one below it) don't work with expressions like `5 + -5`. Still a pretty good answer imo, just need that tiny fix. – Ronen Ness Aug 31 '16 at 06:19

Alex W · Answer 2 · 2013-06-11T19:46:31.907

7

EDIT:

This works like the accepted answer and as a bonus won't fail due to filter() in IE8 and below:

var expression = "7.2*6+3/2-5*6+(7-2)*5";
var splitUp = expression.match(/[^\d()]+|[\d.]+/g);
document.body.innerHTML = splitUp;

http://jsfiddle.net/smAPk/

edited Jun 11 '13 at 19:46

answered Jun 11 '13 at 18:27

Alex W

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Your solution is elegant, but both you and the accepted answer have a bug. the following expression `5 + -1` returns `['5', '+ -', '1']`, which doesn't make much sense.. You still got my upvote though ;) – Ronen Ness Aug 31 '16 at 06:17

score 1 · Answer 3 · answered Jun 11 '13 at 19:01

First of all, if you want to use a regular expression with split() you have to create it first:

var expr = new RegExp("(?<=[-+*/])|(?=[-+*/])")  
// note: you missed a ) at the end

Sadly, the RegExp engine in most browsers doesn't support lookbehinds, so it won't work anyway. You have to do this in a loop.

split a mathematical expression on operators and include the operators in the output array

3 Answers3

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