Question

102

JavaScript flooring number to order of magnitude

rated 0 times [ 104] [ 2] / answers: 1 / hits: 6692 / 10 Years ago, wed, may 28, 2014, 12:00:00

I want to floor any integers >= 10 according to its order of magnitude. For instance,

15 -> 10

600 -> 100

8,547 -> 1,000

32,123 -> 10,000

3,218,748 -> 1,000,000

544,221,323,211 -> 100,000,000,000

....

I was thinking parsing the int to string and count how many digits are there, then set the new string to 1 + a bunch of zeros and convert back to number.

function convert(n) {

    nStr = n.toString();

    nLen = nStr.length;

    newStr = 1 + Array(nLen).join(0);

    return parseInt(newStr);

}

Is there a more mathematical way to do this? I want to avoid converting between int and str because it might waste a lot of memory and disk space when n is huge and if I want to run this function a million times.

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deanna

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answered 10 Years ago alejandro · Accepted Answer

So you're looking for the order of magnitude.

function convert(n) {

    var order = Math.floor(Math.log(n) / Math.LN10

                       + 0.000000001); // because float math sucks like that

    return Math.pow(10,order);

}

Simple ^_^ Math is awesome! Floating point imprecisions, however, are not. Note that this won't be completely accurate in certain edge cases, but it will do its best.