Evaluate polynomial expression string

Question

Create a function which takes a polynomial equation, a value for x and returns the result of the operation.

Example: given 4x^2+2x-5 and x=3 output 37. This is the result of 4(3)^2+2(3)-5

• Assume all polynomials are valid
• Polynomial format will always be coefficient(variable)^exponent => 4x^2 except :
  • When exponent is 1 it will be coefficient(variable) => 4x
  • When coefficient is 1 it will be (variable)^exponent => x^2
• Polynomials are one variable only
• Use of external libraries are forbidden
• The coefficient and variable input can be positive and negative numbers.

Test cases

• ("3x^3-5x^2+2x-10", 5) => 250
• ("10x^4-5x^3-10x^2+3x+50", 3) => 644
• ("10x+20", 10) => 120
• ("-20x^2+20x-50", -8) => -1490
• ("9", 5) => 9
• ("8x^2+5", 0) => 5

---

Update

• Polynomial format will always be coefficient(variable)^exponent => 4x^2 except :
  • When exponent is 1 it will be coefficient(variable) => 4x
  • When coefficient is 1 it will be (variable)^exponent => x^2
• Removed the rule of negative exponent. My mistake. A valid polynomial does not contain negative exponent
• An exponent of 0 would be just coefficient
• Added test case for input 0

---

This is code-golf, so the shortest answer in bytes win.

Answer 1

JavaScript (ES7), 48 bytes

Based upon a suggestion from @RickHitchcock

Expects X in uppercase. Takes input in currying syntax (p)(X).

p=>X=>eval(p.replace(/[X^]/g,c=>c<{}?'*X':'**'))

Try it online!

---

JavaScript (ES7), 49 bytes

Same approach as @DeadPossum. Takes input in currying syntax (p)(x).

p=>x=>eval(p.split`x`.join`*x`.split`^`.join`**`)

Try it online!

Answer 2

Python 2, 54 bytes

-2 bytes thanks to Jo King

-5 bytes thanks to Arnauld

lambda p,x:eval(p.replace('^','**').replace('x','*x'))

Try it online!

Answer 3

Python 3, 53 50 48 bytes

edit: -5 bytes thanks to Dennis !

lambda p,x:eval(p.translate({94:"**",120:"*x"}))

Try it online!

Used translate to avoid chaining replace calls; Python 3's version of translate is less awkward than its predecessor's.

Answer 4

R, 44 bytes

function(f,x)eval(parse(t=gsub("x","*x",f)))

Try it online!

Fairly straightforward with R. Replace nx with n*x and then eval the parsed string. x is used as this is how we name the second argument.

The eval function could even be used more directly with a properly formatted first argument, and other formal arguments (y, z, etc.) could be easily added:

R, 20 bytes (non-competing)

function(f,x)eval(f)

Try it online!

Answer 5

Japt 2.0, 13 bytes

OvUd^'*²'x"*V

Try it.

Explanation:

OvUd^'*²'x"*V
              U = Implicit first input
              V = Implicit second input

Ov            Eval:
  Ud            In U, replace:
    ^             "^" with:
     '*²            "**"
        'x        "x" with:
          "*V       "*V"

Answer 6

Wolfram Language (Mathematica), 22 bytes

ToExpression@#/.x->#2&

Try it online!

Answer 7

JavaScript (Node.js), 113 108 bytes

_=>x=>_.match(/-?(?:[x\d]+|\^?)+/g).reduce((a,b)=>b.split`x`[0]*(~b.indexOf`x`?x**(b.split`^`[1]||1):1)+a,0)

Try it online!

Thanks to @Arnauld

---

Since the best JS solution so far by @Arnauld (49 bytes) has already been posted and it uses eval, I decided to use Regex and reduce instead of that.

Pretty lengthy compared to his though.

Explanation :

A =>                            // lambda function accepting argument 1 
    x =>                        // argument number 2 (currying syntax used)
        A.match(                // this matches all instance of what comes next 
                                // and converts to array
       /[-]?(?:[x\d]+|\^?)+/g)  // regexp for -ve sign , variable number and ^ sign 
            .reduce((a, b) =>   // reduce the array to single (take 2 params a,b)
                b.split `x`     // split b at instances of `x` 
                        [0]     // and select the first instance 
                * (b.indexOf`x` // multiply that by value of index of x in b 
                    > 0 ?       // if it is greater than 0 then 
                x **            // multiplication will be with x raised to power
               (l = b.split `^` // set variable split b at every `x` 
                   [1]||1       // choose first index otherwise set to one
                )               // this is what x is raised to the power 
                : 1)            // in the case x is not present multiply by 1
                + a,            //  add value of `a` to that value 
        0)                      // in case no reduce is possible set value to 0

---

Answer 8

05AB1E, 16 19 bytes

„*(I')J'xs:'^„**:.E

+3 bytes as bug-fix for negative input x.

.E (Run as Batch code) has been replaced with Run as Python eval in this latest commit of @Adnan, but this version isn't on TIO yet. @Mr.Xcoder tested it on his local (latest version) 05AB1E to verify it's working.
See this version without .E to see how it converted the expression string.

Explanation:

„*I')J'xs:    # Replace all "x" with "*(n)" (where `n` is the input-integer)
              #  i.e. 5 and 3x^3-5x^2+2x-10 → 3*(5)^3-5*(5)^2-2*(5)-10
'^„**:        # Replace all "^" with "**"
              #  i.e. 3*(5)^3-5*(5)^2-2*(5)-10 → 3*(5)**3-5*(5)**2-2*(5)-10
.E            # Evaluate as Python-eval
              #  i.e. 3*(5)**3-5*(5)**2-2*(5)-10 → 250

---

Alternative 25 28 bytes program that works on the current version of TIO:

„*(I')J'xs:'^„**:“…¢(“s')J.e

Try it online.

Explanation:

„*(I')J'xs:'^„**:    # Same as explained above
“…¢(“                # Literal string "print("
     s               # Swap both
      ')             # Literal character ")"
        J            # Join everything together
                     #  i.e. 3*(5)**3-5*(5)**2-2*(5)-10 → print(3*(5)**3-5*(5)**2-2*(5)-10)
.e                   # Run as Python code
                     #  i.e. print(3*(5)**3-5*(5)**2-2*(5)-10) → 250

“…¢(“ is the string print(, because:

• “ and “ starts and ends the compressed string
• …¢ is equal to 0426 because it looks at the indices in the info.txt file, where … has index 4, and ¢ has index 26.
• This index 0426 is then used in the dictionary-file, where line 427 (index 426) is the word it fetches, which is print in this case.
• The ( doesn't have an index in the info.txt file, so it is interpret as is.

Answer 9

JavaScript (Node.js), 143 bytes

I know there are better answers but I wanted to do it without using eval

(_,x)=>_.match(/[+-]?(?:[a-z0-9.]+|\^-?)+/gi).reduce((a,b)=>~~(b.split('x')[0])*(b.indexOf('x')>0?Math.pow(x,(l=(b.split('^')[1]))?l:1):1)+a,0)

Try it online!

Answer 10

Physica, 35 bytes

->e;x:Eval@Replace[e;"x";f"*({x})"]

Try it online!

Answer 11

Octave, 47 38 37 bytes

Saved a lot of bytes by taking the second input as a string instead of a number.

@(x,c)eval(strrep(x,'x',['*(',c,41]))

Try it online!

Explanation:

Fairly straight forward: Replace x by (c) , where c is the second input, and evaluate. The paretheses are necessary because in Octave -8^2 == -64.

Answer 12

Java 8, 150 149 148 bytes

n->s->new javax.script.ScriptEngineManager().getEngineByName("JS").eval(s.replace("x","*"+n).replaceAll((s="(\\-?\\d+)")+"\\^"+s,"Math.pow($1,$2)"))

Not sure if it's possible to have a currying lambda function that throws an Exception. If it is, 1 byte can be saved changing (s,n)-> to n->s->. -1 byte thanks to @OlivierGrégoire for showing me how to do this.

Try it online.

Explanation:

n->s->     // Method with integer and String parameters and Object return-type
  new javax.script.ScriptEngineManager().getEngineByName("JS")
            //  Use a JavaScript engine
   .eval(s  //  And eval the input
      .replace("x","*"+n)
            //   After all 'x' has been replaced with '*n'
            //   (where `n` is the input-integer)
      .replaceAll((s="(\\-?\\d+)")+"\\^"+s,"Math.pow($1,$2)"))
            //   And all `A^B` have have been replaced with `Math.pow(A,B)`
            //   (where both `A` and `B` are integers)

Unfortunately the JavaScript eval doesn't support **, so I have to use a longer replace to convert it to Math.pow instead..

Answer 13

Jelly, 21 bytes

ṣ”^j⁾**ṣ”xjØ(j”*;Ʋ}ŒV

Try it online!

Answer 14

TI-Basic, 6 bytes

Prompt X:expr(Ans

Expression is taken as argument and X is entered during runtime. Alternatively 8 bytes without expr:

Prompt X,u:u

Here both arguments are entered at runtime.

Answer 15

Ruby, 43 bytes

->s,x{eval s.gsub /[x^]/,?x=>"*x",?^=>"**"}

Try it online!

Answer 16

Ruby, 43 41 bytes

->p,x{eval p.gsub('^','**').gsub'x','*x'}

Try it online!

Saved two bytes thanks to @Mr.Xcoder

---

Since there isn't a Ruby answer yet I added one. Nvm there was one that used a different approach

Explanation :

->p,x{                    # lambda function that takes two arguments p and x
    eval(                 # eval 
        p.gsub(           # replace all instance of 
            '^' , '**'    # `^` with `**` (use for raised to power of)
        )                 # end gsub
        .gsub(            # start another replace all
            'x' , '*x'    # replace all instances of `x` with `*x`
        )                 # end the replace function
    )                     # end eval function
}                         # end lambda function

Answer 17

Perl 5 -pl, 35 bytes

s/\^/**/g;$q=<>;s/x/*($q)/g;$_=eval

Try it online!

Answer 18

Wolfram Language (Mathematica), 19 bytes

(x=#;ToExpression)&

Try it online!

Take input by currying: f[x][expr].

Answer 19

Excel, 36+2 bytes, Non-competing

Evaluating a Text field as a formula is not straight forward in Excel. There is a hidden =EVALUATE() function, that can be called by defining a Name.

In Excel 2007, Formulas > Define Name. Define a Name called E, with Refers to:

=EVALUATE(SUBSTITUTE(A1,"x","*"&B1))

Then, with Formula input in A1, x value in B1, entering =E in C1 returns expected result.