regular expression to insert * at proper places in an equation

Question

I have an expression such as xsin(x) it is valid only if * comes between x and sin(x) and make it as x*sin(x)

my idea is first search for x then insert * between x and another variable if there is a variable.

equation

sin(x)cos(x) to sin(x)*cos(x)
pow((x),(2))sin(x)to pow((x),(2))*sin(x)
sin(x)cos(x)tan(x) to sin(x)*cos(x)*tan(x)

etc

I am trying with this code..

function cal(str)
{

  //var string = "3*x+56";
  var regex = /([a-z]+)\(\(([a-z]+)\),\(([0-9]+)\)\)\(([a-z0-9\*\+]+)\)([\*\-%\/+]*)/;
  var replacement = "$1($2($4),($3))$5";
  while(str.match(regex))
    {
      str = str.replace(regex,replacement);
    }
  return str;
}

Please give a list of some possible equations (before & after). I assume we are not just talking about `x*sin(x)`? — Nerdwood, Oct 16 '15 at 03:35
if we count the number of open braces '(' and if it is equal to number of close one ')'. Then replace that match with '(anything)*anything_else' only if next char is not an operator. — rhitz, Oct 16 '15 at 04:06
x is a variable, it can be named as x, y, z or even sin.(too complex)..another option you might try is to add functions names(sin,cos,tan,pow etc) in a array and use it with regex. — rhitz, Oct 16 '15 at 05:51

score 2 · Answer 1 · answered Oct 16 '15 at 03:48

2

> 'sin(x)cos(x)'.replace(/(?!^)\w{3}/g, '*$&')
< "sin(x)*cos(x)"
> 'pow((x),(2))sin(x)'.replace(/(?!^)\w{3}/g, '*$&')
< "pow((x),(2))*sin(x)"
> 'sin(x)cos(x)tan(x)'.replace(/(?!^)\w{3}/g, '*$&')
< "sin(x)*cos(x)*tan(x)"

This says: replace anything that doesn't start at the beginning and has three letters with a * and everything that matched

answered Oct 16 '15 at 03:48

qwertymk

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I not sure but seems it wrong for 'x+sin(x)' – Grundy Oct 16 '15 at 03:54
yes Grundy you are correct .it is not working for x+sin(x) – smraj Oct 16 '15 at 04:13

score 2 · Accepted Answer · edited May 23 '17 at 11:44

2

This one matches right parentheses followed by a letter (e.g. )s ), and inserts a * (e.g. )*s )

It also replaces x followed by a letter with x* and that letter

It should work for x+sin(x) and xsin(x)

function addStars(str) {
    return str.replace(/(\))([A-Za-z])/g,function(str, gr1, gr2) { return gr1 + "*" + gr2 }).replace(/x([A-Za-wy-z])/g,function(str, gr1) { return "x*" + gr1 })
}

document.write(addStars("x+sin(x)tan(x)ln(x)+xsin(x)"))

Help from:
JavaScript - string regex backreferences
qwertymk's answer

edited May 23 '17 at 11:44

Community

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1

answered Oct 16 '15 at 03:56

Josiah Krutz

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you are partially correct . i am not getting it correct for xsin(x). – smraj Oct 16 '15 at 04:02
now it is perfec.you are amazing Josiah.Thanks for all others for helping me – smraj Oct 16 '15 at 06:03

regular expression to insert * at proper places in an equation

2 Answers2