Rounding numbers down to 1

Question

What I'm trying to do is round the number to the left down to 1. For instance, if a number is 12345.6789, round down to 100000.0000.. If the number is 9999999.9999, round down to 1000000.0000. Also want this to work with decimals, so if a number is 0.00456789, round it down to 0.00100000.

In this example, 5600/100000 = 0.056 and I want it to round to 0.01. I use the following code in LUA scripts and it works perfectly.

function rounding(num)
  return 10 ^ math.floor((math.log(num))/(math.log(10)))
end
print(rounding(5600/100000))

But if I use the same for Javascript, it returns -11, instead of 0.01.

function rounding(num) {
  return 10 ^ Math.round((Math.log(num))/(Math.log(10)))
}
console.log((rounding(5600/100000)).toFixed(8))

Any help or guidance would be greatly appreciated.

You cannot "12345.6789, round down to 100000.0000", that is up. Same for "9999999.9999, round down to 1000000.0000". — Yunnosch, Mar 24 '20 at 21:05
[`^` is not "to the power of"](https://stackoverflow.com/questions/3618340/javascript-what-does-the-caret-operator-do) — VLAZ, Mar 24 '20 at 21:07
Are you aware of what the `^` operator does? Hint, it is not exponential or power. — Yunnosch, Mar 24 '20 at 21:08

Nina Scholz · Accepted Answer · 2020-03-24T21:13:42.047

0

You could floor the log₁₀ value and get the value back of the exponential value with the base of 10.

The decimal places with zeroes can not be saved.

const format = number => 10 ** Math.floor(Math.log10(number));

var array = [
          12345.6789,     //  100000.0000 this value as a zero to much ...
        9999999.9999,     // 1000000.0000
              0.00456789, //       0.00100000
    ];

console.log(array.map(format));

edited Mar 24 '20 at 21:13

answered Mar 24 '20 at 21:08

Nina Scholz

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Thanks everyone.. I should have been using ** instead of ^. Guess that's one of the many differences between LUA and Javascript. – BlueSuede Mar 24 '20 at 21:27

score 0 · Answer 2 · answered Mar 24 '20 at 21:18

Check this code. It processes characters individually. It seems to do the job.

function rounding(num) {
  const characters = num.toString().split('');
  let replaceWith = '1';
  characters.forEach((character, index) => {
    if (character === '0' || character === '.') {
      return;
    };
    characters[index] = replaceWith;
    replaceWith = '0';
  });
  return characters.join('');
}
console.log(rounding(12345.6789));
console.log(rounding(9999999.9999));
console.log(rounding(0.00456789));
console.log(rounding(5600/100000));

Rounding numbers down to 1

2 Answers2