How to keep Javascript array sorted, without sorting it

Question

I have a Node.js application where I have to very often do following things: - check if particular array already contains certain element - if element does exist, update it - if

Answer 1

If your array is already sorted and you want to insert an element, to keep it sorted you need to insert it at a specific place in the array. Luckily arrays have a method that can do that: Array.prototype.splice

So, once you get the index you need to insert at (you should get by a simple modification to your binary search), you can do:

myArr.splice(myIndex,0,myObj);
// myArr your sorted array
// myIndex the index of the first item larger than the one you want to insert
// myObj the item you want to insert

EDIT: The author of your binary search code has the same idea:

So if you wanted to insert a value and wanted to know where you should put it, you could run the function and use the returned number to splice the value into the array. Source

Answer 2

It's easy to modify this binaryIndexOf function to return an index of the next element when no matches found:

function binaryFind(searchElement) {
  'use strict';

  var minIndex = 0;
  var maxIndex = this.length - 1;
  var currentIndex;
  var currentElement;

  while (minIndex <= maxIndex) {
    currentIndex = (minIndex + maxIndex) / 2 | 0;
    currentElement = this[currentIndex];

    if (currentElement < searchElement) {
      minIndex = currentIndex + 1;
    }
    else if (currentElement > searchElement) {
      maxIndex = currentIndex - 1;
    }
    else {
      return { // Modification
        found: true,
        index: currentIndex
      };
    }
  }      

  return { // Modification
    found: false,
    index: currentElement < searchElement ? currentIndex + 1 : currentIndex
  };
}

So, now it returns objects like:

{found: false, index: 4}

where index is an index of the found element, or the next one.

So, now insertion of a new element will look like:

var res = binaryFind.call(arr, element);
if (!res.found) arr.splice(res.index, 0, element);

Now you may add binaryFind to Array.prototype along with some helper for adding new elements:

Array.prototype.binaryFind = binaryFind;

Array.prototype.addSorted = function(element) {
  var res = this.binaryFind(element);
  if (!res.found) this.splice(res.index, 0, element);
}

Answer 3

I know this is an answer to an old question, but the following is very simple using javascripts array.splice().

function inOrder(arr, item) {
    /* Insert item into arr keeping low to high order */

    let ix = 0;
    while (ix < arr.length) {
        //console.log('ix',ix);
        if (item < arr[ix]) { break; }
        ix++;
    }

    //console.log('  insert:', item, 'at:',ix);
    arr.splice(ix,0,item);
    return arr
}

The order can be changed to high to low by inverting the test