# Proposal: 1) Number (integer or decimal) to Array 2) Array to Number (integer or decimal)

guest271314 guest271314 at gmail.com
Thu Mar 7 21:08:19 UTC 2019

```Ability to adjust *nth* digit of an integer or decimal by adjusting decimal
or integer at *nth* index of array, to try to solve OEIS A217626
oeis.org/A217626 directly, for example
~~(128.625*9*1.074)//1243
~~(128.625*9*1.144)//1324
where the decimal portion can be manipulated by referencing the index of an
array, then converting the array back to a number.

On Thu, Mar 7, 2019 at 8:55 PM Jeremy Martin <jmar777 at gmail.com> wrote:

> Can you explain the motivation for this proposal?
>
> At first blush, this seems like an incredibly arbitrary pair of value
> conversion utilities. Are there real world applications for this?
>
> On Thu, Mar 7, 2019 at 3:43 PM guest271314 <guest271314 at gmail.com> wrote:
>
>>
>>
>> ---------- Forwarded message ---------
>> From: guest271314 <guest271314 at gmail.com>
>> Date: Thu, Mar 7, 2019 at 8:35 PM
>> Subject: Proposal: 1) Number (integer or decimal) to Array 2) Array to
>> Number (integer or decimal)
>> To: <es-discuss at mozilla.org>
>>
>>
>> Original concept: Integer or decimal to array and array to decimal or
>> integer https://codegolf.meta.stackexchange.com/a/17223
>>
>> Proof of concept (with bugs)
>>
>> function numberToArray(n) {
>>
>>   if (Math.abs(n) == 0 || Math.abs(n) == -0) {
>>     return [n]
>>   }
>>
>>   const r = [];
>>
>>   let [
>>     a, int = Number.isInteger(a), d = g = [], e = i = 0
>>   ] = [ n || this.valueOf()];
>>
>>   if (!int) {
>>     let e = ~~a;
>>     d = a - e;
>>     do {
>>       if (d < 1) ++i;
>>       d *= 10;
>>     } while (!Number.isInteger(d));
>>   }
>>
>>   for (; ~~a; r.unshift(~~(a % 10)), a /= 10);
>>
>>   if (!int) {
>>     for (; ~~d; g.unshift(~~(d % 10)), d /= 10);
>>     g[0] = g[0] * (1 * (10 ** -i))
>>     r.push(...g);
>>   }
>>
>>   return r;
>> }
>> function arrayToNumber(a) {
>>   if ((Math.abs(a[0]) == 0 || Math.abs(a[0]) == -0)
>>      && a.length == 1) return a[0];
>>   const [
>>     g, r = x => x.length == 1
>>                 ? x[0]
>>                 : x.length === 0
>>                   ? x
>>                   : x.reduce((a, b) => a + b)
>>     , b = a.find(x => g(x)), p = a.findIndex(x => g(x))
>>   ] = [x => !Number.isInteger(x)];
>>
>>   let [i, j] = [b ? p : a.length, -1];
>>
>>   return a.length === 1
>>     ? a[0]
>>     : b && p
>>       ? r(a.slice(0, p).map(x => i ? x * (10 ** --i) : x))
>>         + (a[p] + (a[p + 1] !== undefined
>>           ? r(a.slice(p + 1).map(x => x * (10 ** --j)))
>>           : 0))
>>       : r(a.map(x => i ? x * (10 ** --i) : x))}
>> let tests = [0, 200, 100.00015, -123, 4.4, 44.44, -0.01, 123
>>             , 2.718281828459, 321.7000000001, 809.56
>>             , 1.61803398874989, 1.999, 100.01, 545454.45
>>             , -7, -83.782, 12, 1.50, 100.0001];
>> let arrays = tests.map(n => [...numberToArray(n)]);
>> let numbers = arrays.map(n => arrayToNumber(n));
>>
>> console.log({tests, arrays, numbers});
>>
>>
>> and working code (fixed bugs) by Stack Overflow user Shidersz
>> https://stackoverflow.com/users/10366495/shidersz
>>
>> Method numberToArray():
>>
>> I have been working some time on your implementation, and thinked to
>> first analyze the numberToArray() method. To start, I have decided to
>> create a method for analyze a decimal number and return statistics about
>> it, basically, the information you where getting from this part of your
>> code:
>>
>> if (!int) {
>>     let e = ~~a;
>>     d = a - e;
>>     do {
>>         if (d < 1) ++i;
>>         d *= 10;
>>     } while (!Number.isInteger(d));}
>>
>> The method I have made on is the next one (will be used inside
>> numberToArray()) and basically gets the next information:
>>
>> *1)* Integer section (iSection) of the decimal number (as integer).
>>
>> *2)* Decimal section (dSection) of the decimal number (as integer).
>>
>> *3)* Number of digits after the dot (dDigits).
>>
>> *4)* Number of leading zeros after the dot (dZeros).
>>
>> function getDecimalStats(dec){
>>     let dDigits = 0, test = dec, factor = 1, dZeros = 0;
>>
>>     // Store the integer section of the decimal number.
>>
>>     let iSection = ~~dec;
>>
>>     // Get the numbers of digits and zeros after the comma.
>>
>>     while (!Number.isInteger(test))
>>     {
>>         factor = Math.pow(10, ++dDigits);
>>         test = dec * factor;
>>         dZeros += Math.abs(test - (iSection * factor)) < 1 ? 1 : 0;
>>     }
>>
>>     // Store the decimal section as integer.
>>
>>     let dSection = test - (iSection * factor);
>>
>>     // Return an object with all statistics.
>>
>>     return {iSection, dSection, dZeros, dDigits};};
>>
>> console.log(getDecimalStats(10.001));
>> console.log(getDecimalStats(-210.1));
>> console.log(getDecimalStats(-0.00001));
>>
>> Of course, if you dislike, you can put this same logic directly inside
>> numberToArray() method. So, after making the previous function, I have
>> done some reorganization on your code and added some commentaries to helps
>> me understand what you where doing. Finally, and after adapted your code, I
>> have found that the wrong mapping to the arrays was mostly because the
>> arithmetic precision when operating with float number. After investigate
>> mathematical correction factor (it is commented on the code when it is
>> applied). All in all, and until this time, I have come with the next
>> solution to the numberToArray() method.
>>
>> function getDecimalStats(dec){
>>     let dDigits = 0, test = dec, factor = 1, dZeros = 0;
>>
>>     // Store the integer section of the decimal number.
>>
>>     let iSection = ~~dec;
>>
>>     // Get the numbers of digits and zeros after the comma.
>>
>>     while (!Number.isInteger(test))
>>     {
>>         factor = Math.pow(10, ++dDigits);
>>         test = dec * factor;
>>         dZeros += Math.abs(test - (iSection * factor)) < 1 ? 1 : 0;
>>     }
>>
>>     // Store the decimal section as integer.
>>
>>     let dSection = test - (iSection * factor);
>>
>>     // Return an object with all statistics.
>>
>>     return {iSection, dSection, dZeros, dDigits};};
>> function numberToArray(n){
>>     let r = [];
>>
>>     if (Math.abs(n) == 0)
>>         return [n];
>>
>>     let [a, int = Number.isInteger(a), g = []] = [n || this.valueOf()];
>>
>>     // Get the stats of the decimal number.
>>
>>     let {dSection, dZeros} = getDecimalStats(a);
>>
>>     // Push the integer part on the array.
>>
>>     for (; ~~a; r.unshift(~~(a % 10)), a /= 10);
>>
>>     // Push the decimal part on the array.
>>
>>     if (!int)
>>     {
>>         // Push decimal digits on temporal array "g".
>>         for (; ~~dSection; g.unshift(~~(dSection % 10)), dSection /= 10);
>>
>>         // Define the correction factor for the next operation.
>>         let cf = 10 ** (++dZeros);
>>
>>         // Map g[0] to a decimal number and push elements on the array.
>>         g[0] = (g[0] * cf) * ((10 ** -dZeros) * cf) / (cf * cf);
>>         r.push(...g);
>>     }
>>
>>     return r;}
>> let tests = [0, 200, 100.00015, -123, 4.4, 44.44, -0.01, 123,2.718281828459, 321.7000000001, 809.56,1.61803398874989, 1.999, 100.01, 545454.45,-7, -83.782, 12, 1.50, 100.0001];
>> let arrays = tests.map(n => [...numberToArray(n)]);
>> console.log({tests, arrays});
>>
>> Method arrayToNumber():
>>
>> For this one I decided to go on my own (actually ignoring your current
>> logic). The next approach will use the previously mentioned
>> getDecimalStats() and mainly the Array::reduce()
>> <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce>
>> :
>>
>> function getDecimalStats(dec){
>>     let dDigits = 0, test = dec, factor = 1, dZeros = 0;
>>
>>     // Store the integer section of the decimal number.
>>
>>     let iSection = ~~dec;
>>
>>     // Get the numbers of digits and zeros after the comma.
>>
>>     while (!Number.isInteger(test))
>>     {
>>         factor = Math.pow(10, ++dDigits);
>>         test = dec * factor;
>>         dZeros += Math.abs(test - (iSection * factor)) < 1 ? 1 : 0;
>>     }
>>
>>     // Store the decimal section as integer.
>>
>>     let dSection = test - (iSection * factor);
>>
>>     // Return an object with all statistics.
>>
>>     return {iSection, dSection, dZeros, dDigits};};
>> function arrayToNumber(a){
>>     // Get the index of the first decimal number.
>>
>>     let firstDecIdx = a.findIndex(
>>         x => Math.abs(x) > 0 && Math.abs(x) < 1
>>     );
>>
>>     // Get stats about the previous decimal number.
>>
>>     let {dZeros} = getDecimalStats(firstDecIdx >= 0 ? a[firstDecIdx] : 0);
>>
>>     // Normalize firstDecIdx.
>>
>>     firstDecIdx = firstDecIdx < 0 ? a.length : firstDecIdx;
>>
>>     // Reduce the array to get the number.
>>
>>     let number = a.reduce(
>>         ({num, dIdx, dPow}, n, i) =>
>>         {
>>             // Define the correction factor.
>>             let cf = 10 ** (dPow + i - dIdx);
>>
>>             if (i < dIdx)
>>                num += n * (10 ** (dIdx - i - 1));
>>             else if (i === dIdx)
>>                num = ((num * cf) + (n * cf)) / cf;
>>             else
>>                num = ((num * cf) + n) / cf;
>>
>>             return {num, dIdx, dPow};
>>         },
>>         {num: 0, dIdx: firstDecIdx, dPow: ++dZeros}
>>     );
>>
>>     return number.num;}
>> let tests = [
>>     [0],
>>     [2, 0, 0],
>>     [1, 0, 0, 0.0001, 5],
>>     [-1, -2, -3],
>>     [4, 0.4],
>>     [4, 4, 0.4, 4],
>>     [-0.01],
>>     [1, 2, 3],
>>     [2, 0.7, 1, 8, 2, 8, 1, 8, 2, 8, 4, 5, 9],
>>     [3, 2, 1, 0.7, 0, 0, 0, 0, 0, 0, 0, 0, 1],
>>     [8, 0, 9, 0.5, 6],
>>     [1, 0.6, 1, 8, 0, 3, 3, 9, 8, 8, 7, 4, 9, 8, 9],
>>     [1, 0.9, 9, 9],
>>     [1, 0, 0, 0.01],
>>     [5, 4, 5, 4, 5, 4, 0.4, 5, 0],
>>     [-7],
>>     [-8,-3, -0.7, -8, -2],
>>     [1, 2],
>>     [1, 0.5],
>>     [1, 0, 0, 0.0001]];
>> let numbers = tests.map(n => arrayToNumber(n));
>> console.log(numbers);
>>
>> Finally, I hope you can value my efforts, and obviously there can be a
>> lot of improvements to my solution (so, any recommendation is welcome). For
>> example, there are currently none or few checks for safety.
>>
>>
>> Number (integer or decimal) to array, array to number (integer or
>> decimal) without using strings https://stackoverflow.com/q/54433007
>>
>> *Context and use cases:*
>>
>> available in some browsers, though not a BigDecimal. The conversion from
>> integer or decimal to array and array to integer or decimal should be
>> possible using the JavaScript programming language. The input and output
>> should not need to be converted to a string during the procedure.
>>
>> Ability to adjust *nth* digit of an integer or decimal by adjusting
>> decimal or integer at *nth* index of array, to try to solve OEIS A217626
>> <https://oeis.org/A217626> directly, for example
>>
>> ~~(128.625*9*1.074)//1243~~(128.625*9*1.144)//1324
>>
>> where the decimal portion can be manipulated by referencing the index of
>> an array, then converting the array back to a number.
>>
>> Specification (WIP):
>>
>> [...Math.E] -> [2, 0.7, 1, 8, 2, 8, 1, 8, 2, 8, 4, 5, 9] -> 2.718281828459
>>
>> Input <----------> Output
>> -123               [-1,-2,-3]4.4                [4,0.4]44.44              [4,4,0.4,4]-0.01              [-0.01]123                [1,2,3]200                [2,0,0]2.718281828459     [2,0.7,1,8,2,8,1,8,2,8,4,5,8,9]321.7000000001     [3,2,1,0.7,0,0,0,0,0,0,0,0,1]809.56             [8,0,9,0.5,6]1.61803398874989   [1,0.6,1,8,0,3,3,9,8,8,7,4,9,8,9]1.999              [1,0.9,9,9]100.01             [1,0,0,0.01]545454.45          [5,4,5,4,5,4,0.4,5]-7                 [-7]-83.782            [-8,-3,-0.7,-8,-2]1.5                [1,0.5]100.0001           [1,0,0,0.0001]
>>
>> _______________________________________________
>> es-discuss mailing list
>> es-discuss at mozilla.org
>> https://mail.mozilla.org/listinfo/es-discuss
>>
>
>
> --
> Jeremy Martin
> 661.312.3853
> @jmar777 <https://twitter.com/jmar777> / @j <https://stream.live/j>
>
>
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