Incrementing function-CodePudding

I am currently trying to create a function that increment numbers. The thing is that I would like the function to be able to change the incrementing value each time a "power of ten" is reached. I have a first function that handle the "incrementing value".

Here is what I have so far:

function getInc(num) {
    let abs = Math.abs(num);
    let inc = Math.pow(10, Math.floor(Math.log10(abs)));
    if (abs === num) return inc;
    if (num === -10) { return -1; }
    if (num === -1) { return -0.1; } 
    return -inc
  }

This works well, except from values likes -10, -0.1. For : getInc(-0.1) the result should be -0.01, but my current function returns -0.1 I would like to avoid lines like if (num === -10) { return -1; } because I can not handle all the cases this way, but I am a little stuck here.

Thank you in advance.

Edit: this is the rest of the code, the function that actually increments, if this can help understand how the getInc result is used:

    if ((num < -1) && (num >= -10) ) {
        return  Math.floor(Math.round(num) - getInc(num))
    }
    if ((num <= 0) && (num >= -1) ) {
        return num - getInc(num)
    }

    if (num >= 1 && num < 10) {
        return  Math.round(Math.floor(num   getInc(num))) ;
    }

    if ((num >= 10) || (num > 0 && num < 1)) {
        const result =   Math.ceil(num / getInc(num)) * getInc(num);
        if (result === num)  { return num   getInc(num) }
        else { return result }
    }

    if (num < -10) {
        const result = Math.ceil(num / getInc(num)) * getInc(num)  - getInc(num);
        if (result === num)  { return num   getInc(num) }
        else { return result }
    }
    
}

Desired results example:

getInc(-10) :  -1
getInc(-4) : -1
getInc(-1) : -0.1
getInc(-0.4) : -0.1
getInc(-0.1) : -0.01
getInc(-0.04) : -0.01
getInc(-0.01) : -0.001

For now I have:

getInc(-10) :  -10
getInc(-4) : -1
getInc(-1) : -1
getInc(-0.4) : -0.1
getInc(-0.1) : -0.1
getInc(-0.04) : -0.01
getInc(-0.01) : -0.01

CodePudding user response：

You could check the sign if the log value is an integer.

function getInc(num) {
    const
        sign = Math.sign(num),
        log = Math.log10(Math.abs(num));

    return sign * Math.pow(10, Math.floor(log) - (sign === -1 && Number.isInteger(log)));
}

console.log(getInc(9));  //  1
console.log(getInc(10)); // 10

console.log(getInc(-10));   // -1     adjust - 1
console.log(getInc(-4));    // -1
console.log(getInc(-1));    // -0.1   adjust - 1
console.log(getInc(-0.4));  // -0.1
console.log(getInc(-0.1));  // -0.01  adjust - 1
console.log(getInc(-0.04)); // -0.01
console.log(getInc(-0.01)); // -0.001 adjust - 1

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CodePudding user response：

your problem are, that numbers, that are already a power of ten are not changed by the expression Math.pow(10, Math.floor(Math.log10(abs))) (because of Math ... if num === power of 10 --> Math.log10(num) === integer (not float) ---> Math.flat() has no effect on integers --> the expression remaining is Math.pow(10, Math.log10(num)) which is the same as just num)

But you want numbers, that already are a power of ten to return a power of ten (but the exponent being one lower as the exponent of num - in easy words, you want the number to get divided by ten)

so at the start of your function you check for numbers, that already are a power of ten ... if that is the case, return the number divided by ten if it is not already a power of ten proceed as it did before.

So your code basically stays the same (you just exit the function early in case of numbers already being a power of ten (and return the number divided by ten)

here's your code with the if clause implemented:

function getInc(num) {
  let abs = Math.abs(num);
  if (Math.log10(abs) % 1 === 0) return num / 10;
  let inc = Math.pow(10, Math.floor(Math.log10(abs)));
  if (abs === num) return inc;
  return -inc;
}

console.log(getInc(100));
console.log(getInc(4));
console.log(getInc(0.1));
console.log(getInc(-4));
console.log(getInc(-1));
console.log(getInc(-0.4));
console.log(getInc(-0.1));