Find out the maximum number of decimal places within a string of numbers

Question

The string looks like this like something along the lines of 3*2.2or 6+3.1*3.21 or (1+2)*3,1+(1.22+3) or 0.1+1+2.2423+2.1 it can vary a bit. I have to find the amount of decimal places in the number inside the string with the most decimal places.

Im totally helpless on how to do it

Ivar · Accepted Answer · 2020-07-28T10:09:26.033

You can use a regular expression to find all numbers that have decimal places and then use Array.prototype.reduce to find the highest amount of decimal places.

const input = '0.1+1+2.2423+2.1';

const maxNumberOfDecimalPlaces = input
  .match(/((?<=\.)\d+)/g)
  ?.reduce((acc, el) =>
    acc >= el.length ?
    acc :
    el.length, 0) ?? 0;

console.log(maxNumberOfDecimalPlaces);

Note that this will return 0 when no numbers with decimal places are found in the string.

Yevhen Horbunkov · Answer 2 · 2020-07-28T16:59:44.437

2

You may do the following:

Array.prototype.split() your input string by RegExp /\[^\d.\]+/ to extract numbers
traverse resulting array of numbers with Array.prototype.map() and split those by decimal separator into whole and fractional parts, returning the length of the fractional part or 0 (for integers)
use Math.max() to find the maximum length

Above method seems to be more robust as it does not involve certain not well supported features:

RegExp lookbehinds assertions (/(?<=)/) which may not be supported by certain popular browsers like Safari or Firefox (below current version)
latest features, like conditional chaining (.?) or nulish coalescing (??)

const src = ['3*2.2', '6+3.1*3.21', '(1+2)*3' , '1+(1.22+3)', '0.1+1+2.2423+2.1'],

      maxDecimals = s => 
       Math.max(
        ...s
          .split(/[^\d.]+/)
          .map(n => {
            const [whole, fract] = n.split('.')
            return fract ? fract.length : 0
          })
       )
      
        
src.forEach(s => console.log(`Input: ${s}, result: ${maxDecimals(s)}`))

.as-console-wrapper{min-height:100%;}

edited Jul 28 '20 at 16:59

answered Jul 28 '20 at 09:53

Yevhen Horbunkov

14,965
3
20
42

yes works perfectly thanks =) now im off to understanding it :) – Sofia Jul 28 '20 at 10:17
1

@Sofia : I have re-factored my answer to be more robust as it had certain compatibility issues, ***just like the answer you currently marked accepted have*** – Yevhen Horbunkov Jul 28 '20 at 17:02
my problem was simply that it was not easily understandable for me, i needed the decimal number as a variable to work with and couldnt figure it out quickly how to do – Sofia Jul 30 '20 at 11:20
@Sofia : in my current solution there's a `fract` variable that holds fractional part of floats, and it uses very basic RegExp which is much easier to comprehend than lookbehind assertions, the rest of it are very basic `.split()` and `.map()`, so if it seems to you that in addition to being more robust (***since other two solutions may simply fail in some popular browsers***) my current solution is more comprehensive, feel free to re-accept. – Yevhen Horbunkov Jul 30 '20 at 11:25
okay i will try it out now... im about to ask another question about a problem with regex im having x] – Sofia Jul 30 '20 at 11:28

Sven.hig · Answer 3 · 2020-07-28T10:15:57.070

1

You could use regex pattern

var str="6+3.1*3.21"
d=str.match(/(?<=\d)[.]\d{1,}/g)
d!=null ? res=d.map((n,i) => ({["number" + (i+1) ] : n.length - 1}))
: res = 0
console.log(res)

edited Jul 28 '20 at 10:15

answered Jul 28 '20 at 09:43

Sven.hig

4,449
2
8
18

Find out the maximum number of decimal places within a string of numbers

3 Answers3