使用C＃替换数学表达式中的变量

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?

Answer 1

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 "$...".TrimStart('$')

Answer 2

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");

Answer 3

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

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

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