Replace variables in a mathematical expression using c#

Question

I have a mathematical expression like following format.

var exp = $(x)+$(y)-tan($(z));

using this I get x,y,z in an array

var dArray = Regex.Split(str, @"[^a-z\.]+").Where(c => c != "." && c.Trim() != "").ToList();

But I am trying to remove '$()' from equation first and then want to replace x,y and z variables. For example

first --> x+y-tan(z)
second --> 5+6-tan(7)

Any solution?

vidstige · Accepted Answer · 2017-10-17 09:53:33Z

3

Just use Math.net something like this

var expression = Infix.ParseOrThrow("x+y-tan(z)")
var symbols = new Dictionary<string,FloatingPoint>
   {{ "x", 5 }, { "y", 6 }, { "z", 7 },};
Evaluate.Evaluate(symbols, expression).RealValue;

To get rid of the $ sign, just do "$...".TrimStart('$')

edited Oct 17, 2017 at 9:53

answered Oct 17, 2017 at 5:42

vidstige

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4 Comments

Nithin Mohan Over a year ago

How to remove '$()'?

Gilad Green Over a year ago

the () jsut leave it doesn't influence and the $ just string.Replace with an empty string

Nithin Mohan Over a year ago

is there possible to add custom symbols like a1,a2 etc? When I tried to evaluate a1+ a2 using 'Infix.ParseOrThrow' it get error

vidstige Over a year ago

No, sadly I think you can only have letters in the symbols

Anthony McGrath · Accepted Answer · 2017-10-17 06:17:36Z

1

How about the below regex replace code. It uses a capture group to obtain the letter inside $()

string exp = "$(x)+$(y)-tan($(z))";
string pattern =  @"\$\((\D)\)";

Regex rgx = new Regex(pattern);
string newExp = rgx.Replace(exp, "$1");
newExp = newExp.Replace("x", "5").Replace("y", "6").Replace("z", "7");

answered Oct 17, 2017 at 6:17

Anthony McGrath

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Comments

user557597 · Accepted Answer · 2017-10-17 05:47:02Z

0

A simple find \$$([^()]*)$
and replace $1

should remove the $() while preserving it's contents.

 \$\(
 ( [^()]* )                    # (1)
 \)

answered Oct 17, 2017 at 5:47

user557597

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