miroiu/string-math

Evaluates a math expression from a string. Supports variables and custom operators.

V3 README can be found here: https://github.com/miroiu/string-math/tree/release-3.0.0

NEW! Boolean math example: https://github.com/miroiu/string-math/pull/6/files

String Math

Calculates the value of a math expression from a string returning a double. Supports variables, user defined operators and expression compilation.

double result = "1 * (2 - 3) ^ 2".Eval(); // 1

Variables

double result = "{a} + 2 * {b}".Substitute("a", 2).Substitute("b", 3).Result; // 8

Global variables

These variables are inherited and cannot be substituted.

MathExpr.AddVariable("PI", 3.1415926535897931);
double result = "1 + {PI}".Eval(); // 4.1415926535897931

Custom operators

Global operators

These operators are inherited and can be overidden.

MathExpr.AddOperator("abs", a => a > 0 ? a : -a);
double result = "abs -5".Eval(); // 5

// Operator precedence (you can specify an int for precedence)
MathExpr.AddOperator("max", (a, b) => a > b ? a : b, Precedence.Power);
double result = new MathExpr("2 * 3 max 4").Result; // 8

Local operators

These are applied only to the target expression.

MathExpr expr = "{PI} + 1";
expr.SetOperator("+", (a, b) => Math.Pow(a, b));
double result = expr; // 3.1415926535897931

double result2 = "{PI} + 1".Eval(); // 4.1415926535897931

Advanced

Extract variables

var expr = "{a} + {b} + {PI}".ToMathExpr();
var variables = expr.Variables; // { "a", "b", "PI" }
var localVariables = expr.LocalVariables; // { "a", "b" }

Compilation

Func<double, double> fn = "{a} + 2".ToMathExpr().Compile("a");
double result = fn(5); // 7

Conditional substitution

MathExpr expr = "1 / {a}".Substitute("a", 1);

double temp = expr.Result; // 1

if (someCondition)  // true
 expr.Substitute("a", 2);

double final = expr.Result; // 0.5

Sharing math context

MathExpr expr = "{PI} + 1";
expr.SetOperator("+", (a, b) => Math.Pow(a, b));

MathExpr expr2 = "3 + 2".ToMathExpr(expr.Context);

double result = "1 + 2 + 3".Eval(expr.Context);

Custom math context

var context = new MathContext(); // new MathContext(MathContext.Default); // to inherit from global
context.RegisterBinary("+", (a, b) => Math.Pow(a, b));

MathExpr expr = new MathExpr("{PI} + 1", context);
MathExpr expr2 = "3 + 2".ToMathExpr(context);
double result = "1 + 2 + 3".Eval(context);

Default operators

Binary

+ (addition)
- (subtraction)
* (multiplication)
/ (division)
% (remainder)
^ (power)
log (logarithm)
max (maximum)
min (minimum)

Unary

- (negation)
! (factorial)
sqrt (square root)
sin (sine)
asin (arcsine)
cos (cosine)
acos (arccosine)
tan (tangent)
atan (arctangent)
rad (convert degrees to radians)
deg (convert radians to degrees)
ceil (ceiling)
floor (floor)
round (rounding)
exp (e raised to power)
abs (absolute)

string-math's Issues

Expression compilation refering to PI global variable.

Based on one of the examples:

        var try1 = "{a} + 2 + {PI}".ToMathExpr();
        var res1 = try1.Substitute("a", 5).Result;

This evaluates as expected, evidently PI exists as a global variable. Trying to compile this to a function doesn't go so well:

        Func<double, double> fn = "{a} + 2 + {PI}".ToMathExpr().Compile("a");
        double result = fn(5); // 7 + PI

This throws an exception at the Compile stage with "Variable 'PI' does not exist.".

Should this work, or am I missing something? Sorry, new to StringMath, trying to get to grips.

Building with 4.1.1.

Thanks!

Duncan

Will you support Boolean expression?

This is a great project!
Will you support Boolean expression?

Question about conditionals.

Hi Emanuel-

Looking at how to handle conditionals, as not everything maps to linear functions. I'd really like a fn (a,b,c) which returns b if a else c, or functionality equivalent to a ? b : c

I don't see anything supporting that in the framework. Lunchtime hacking turned up the below.

If this approach is good, it may be worth including in examples. If not, what is the recommended approach, and is a ternary operator a reasonable feature request?

Thanks!

Duncan

        context.RegisterLogical("<=", (a, b) => a <= b, Precedence.Addition);
        context.RegisterLogical(">", (a, b) => a > b, Precedence.Addition);

        context.RegisterBinary("if",(a,b) => (b != 0) ? a : 0, Precedence.Addition);

        MathExpr expr = new MathExpr("({x} if {x} <= 0.5) + (({x} - 0.5) if ({x} > 0.5))", context);

        var fn = expr.Compile("x");

        Debug.Assert(IsNear(fn(0.0), 0));
        Debug.Assert(IsNear(fn(0.75), 0.25));

Exception thrown for expressions with scientific notation (e.g. "1e2d")

Just a heads up:
An exception is thrown when attempting to execute the following command:
"1e2d".Eval()

Unexpected token e at position 2. Expected [EOC]

The exception is thrown at

at StringMath.Parser.Parse() at StringMath.MathExprExtensions.Eval(String value)

Cheers

Can this support hex integer expression, like `0xaa` ?

I need to eval an expression like this: 0x600+8 , it's expected to be 0x608 ,equals 1544.
Can this project currently achieve this function? If not, can you please implement it ?