将分数字符串转换为十进制？

Question

I'm trying to create a javascript function that can take a fraction input string such as '3/2' and convert it to decimal—either as a string '1.5' or number 1.5

function ratio(fraction) {
    var fraction = (fraction !== undefined) ? fraction : '1/1',
    decimal = ??????????;
    return decimal;
});

Is there a way to do this?

Answer 1

Since no one has mentioned it yet there is a quick and dirty solution:

var decimal = eval(fraction); 

Which has the perks of correctly evaluating all sorts of mathematical strings.

eval("3/2")    // 1.5
eval("6")      // 6
eval("6.5/.5") // 13, works with decimals (floats)
eval("12 + 3") // 15, you can add subtract and multiply too

People here will be quick to mention the dangers of using a raw eval but I submit this as the lazy mans answer.

Answer 2

Here is the bare bones minimal code needed to do this:

var a = "3/2";
var split = a.split('/');
var result = parseInt(split[0], 10) / parseInt(split[1], 10);
alert(result); // alerts 1.5

JsFiddle: http://jsfiddle.net/XS4VE/

Things to consider:

• division by zero
• if the user gives you an integer instead of a fraction, or any other invalid input
• rounding issues (like 1/3 for example)

Answer 3

I created a nice function to do just that, everything was based off of this question and answers but it will take the string and output the decimal value but will also output whole numbers as well with out errors

https://gist.github.com/drifterz28/6971440

function toDeci(fraction) {
    fraction = fraction.toString();
    var result,wholeNum=0, frac, deci=0;
    if(fraction.search('/') >=0){
        if(fraction.search('-') >=0){
            wholeNum = fraction.split('-');
            frac = wholeNum[1];
            wholeNum = parseInt(wholeNum,10);
        }else{
            frac = fraction;
        }
        if(fraction.search('/') >=0){
            frac =  frac.split('/');
            deci = parseInt(frac[0], 10) / parseInt(frac[1], 10);
        }
        result = wholeNum+deci;
    }else{
        result = fraction
    }
    return result;
}

/* Testing values / examples */
console.log('1 ',toDeci("1-7/16"));
console.log('2 ',toDeci("5/8"));
console.log('3 ',toDeci("3-3/16"));
console.log('4 ',toDeci("12"));
console.log('5 ',toDeci("12.2"));

Answer 4

Something like this:

bits = fraction.split("/");
return parseInt(bits[0],10)/parseInt(bits[1],10);

Answer 5

I have a function I use to handle integers, mixed fractions (including unicode vulgar fraction characters), and decimals. Probably needs some polishing but it works for my purpose (recipe ingredient list parsing).

• NPM
• GitHub

Inputs "2 1/2" , "2½" , "2 ½" , and "2.5" will all return 2.5 . Examples:

var numQty = require("numeric-quantity");

numQty("1 1/4") === 1.25;  // true
numQty("3 / 4") === 0.75;  // true
numQty("¼" ) === 0.25;     // true
numQty("2½") === 2.5;      // true
numQty("¾") === 0.75;      // true
numQty("⅓") === 0.333;     // true
numQty("⅔") === 0.667;     // true

One thing it doesn't handle is decimals within the fraction, eg "2.5 / 5" .

Answer 6

Too late, but can be helpful:

You can use Array.prototype.reduce instead of eval https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

ES6

const fractionStrToDecimal = str => str.split('/').reduce((p, c) => p / c);
console.log(fractionStrToDecimal('1/4/2')); // Logs 0.125
console.log(fractionStrToDecimal('3/2')); // Logs 1.5

CJS

function fractionStrToDecimal(str) {
  return str.split('/').reduce((p, c) => p / c);
}
console.log(fractionStrToDecimal('1/4')); // Logs 0.25

[EDIT] Removed reducer initial value and now the function works for numerators greater than 1. Thanks, James Furey.

Answer 7

Function (ES6):

function fractionToDecimal(fraction) {
  return fraction
    .split('/')
    .reduce((numerator, denominator, i) =>
      numerator / (i ? denominator : 1)
    );
}

Function (ES6, condensed):

function fractionToDecimal(f) {
  return f.split('/').reduce((n, d, i) => n / (i ? d : 1));
}

Examples:

fractionToDecimal('1/2');     // 0.5
fractionToDecimal('5/2');     // 2.5
fractionToDecimal('1/2/2');   // 0.25
fractionToDecimal('10/5/10'); // 0.2
fractionToDecimal('0/1');     // 0
fractionToDecimal('1/0');     // Infinity
fractionToDecimal('cat/dog'); // NaN

Answer 8

If you don't mind using an external library, math.js offers some useful functions to convert fractions to decimals as well as perform fractional number arithmetic.

 console.log(math.number(math.fraction("1/3"))); //returns 0.3333333333333333 console.log(math.fraction("1/3") * 9) //returns 3

 <script src="https://cdnjs.cloudflare.com/ajax/libs/mathjs/3.20.1/math.js"></script>

Answer 9

To convert a fraction to a decimal, just divide the top number by the bottom number. 5 divided by 3 would be 5/3 or 1.67. Much like:

function decimal(top,bottom) {
    return (top/bottom)
}

Hope this helps, haha

Answer 10

It works with eval() method but you can use parseFloat method. I think it is better! Unfortunately it will work only with that kind of values - "12.2" not with "5/8", but since you can handle with calculation I think this is good approach!

Answer 11

If you want to use the result as a fraction and not just get the answer from the string, a library like https://github.com/infusion/Fraction.js would do the job quite well.

var f = new Fraction("3/2");
console.log(f.toString()); // Returns string "1.5"
console.log(f.valueOf()); // Returns number 1.5

var g = new Fraction(6.5).div(.5);
console.log(f.toString()); // Returns string "13"

Answer 12

Also a bit late to the party, but an alternative to eval() with less security issues (according to MDN at least) is the Function() factory.

var fraction = "3/2";
console.log( Function("return (" + fraction + ");")() );

This would output the result "1.5" in the console.

Also as a side note: Mixed fractions like 1 1/2 will not work with neither eval() nor the solution with Function() as written as they both stumble on the space.

Answer 13

safer eval() according to MDN

const safeEval = (str) => {
   return Function('"use strict";return (' + str + ")")();
}

safeEval("1 1/2") // 1.5

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#Do_not_ever_use_eval !

Answer 14

This too will work:

let y = "2.9/59"
let a = y.split('')
let b = a.splice(a.indexOf("/"))
console.log(parseFloat(a.join('')))
a = parseFloat(a.join(''))
console.log(b)
let c = parseFloat(b.slice(1).join(''))
let d = a/c
console.log(d) // Answer for y fraction

Answer 15

 const fractionStringToNumber = s => s.split("/").map(s => Number(s)).reduce((a, b) => a / b); console.log(fractionStringToNumber("1/2")); console.log(fractionStringToNumber("1/3")); console.log(fractionStringToNumber("3/2")); console.log(fractionStringToNumber("3/1")); console.log(fractionStringToNumber("22/7")); console.log(fractionStringToNumber("355 / 113")); console.log(fractionStringToNumber("8/4/2")); console.log(fractionStringToNumber("3")); // => 3, not "3"

Answer 16

From a readability, step through debugging perspective, this may be easier to follow:

// i.e. '1/2' -> .5
// Invalid input returns 0 so impact on upstream callers are less likely to be impacted
function fractionToNumber(fraction = '') {
    const fractionParts = fraction.split('/');
    const numerator = fractionParts[0] || '0';
    const denominator = fractionParts[1] || '1';
    const radix = 10;
    const number = parseInt(numerator, radix) / parseInt(denominator, radix);
    const result = number || 0;

    return result;
}

Answer 17

I developed a function to convert a value using a factor that may be passed as a fraction of integers or decimals. The user input and conversion factor might not be in the correct format, so it checks for the original value to be a number, as well as that the conversion can be converted to a fraction assuming that /number means 1/number, or there are a numerator and a denominator in the format number/number.

/**
 * Convert value using conversion factor
 * @param {float} value - number to convert
 * @param {string} conversion - factor
 * @return {float} converted value
 */
function convertNumber(value, conversion) {
  try {
    let numberValue = eval(value);
    if (isNaN(numberValue)) {
      throw value + " is not a number.";
    }
    let fraction = conversion.toString();
    let divider = fraction.indexOf("/");
    let upper = 1;
    let denominator = 1;
    if (divider == -1) {
      upper = eval(fraction);
    } else {
      let split = fraction.split("/");
      if (split.length > 2) {
        throw fraction + " cannot be evaluated to a fraction.";
      } else {
        denominator = eval(split[1]);
        if (divider > 0) {
          upper = eval(split[0]);
        }
      }
    }
    let factor = upper/denominator;
    if (isNaN(factor)) {
      throw fraction + " cannot be converted to a factor.";
    }
    let result = numberValue * factor;
    if (isNaN(result)) {
      throw numberValue + " * " + factor + " is not a number.";
    }
    return result
  } catch (err) {
    let message = "Unable to convert '" + value + "' using '" + conversion + "'. " + err;
    throw message;
  }
}

Answer 18

You can use eval() with regex to implement a secure method to calculate fraction

var input = "1/2";
return input.match(/^[0-9\/\.]+$/) != null ? eval(input) : "invalid number";

Answer 19

With modern destructuring syntax, the best/safest answer can be simplified to:

const parseFraction = fraction => {
  const [numerator, denominator] = fraction.split('/').map(Number);
  return numerator / denominator;
}

// example
parseFraction('3/2'); // 1.5

In other words, split the faction by its / symbol, turn both resulting strings into numbers, then return the first number divided by the second...

... all with only two (very readable) lines of code.