removing duplicate entries from an array and arranging in order in javascript

Question

I want to remove all the duplicate items in the array and arrange them in order of their occurrence from most to least

["57358e5dbd2f8b960aecfa8c",
"573163a52abda310151e5791",
"573163a52abda310151e5791",
"573163a52abda310151e5791",
"573163a52abda310151e5791",
"573163da2abda310151e5792",
"57358e5dbd2f8b960aecfa8c",
"57358e5dbd2f8b960aecfa8c"
"573163da2abda310151e5792",]

I want like this

["573163a52abda310151e5791",
 "57358e5dbd2f8b960aecfa8c",
 "573163da2abda310151e5792"]

as the 1st one appears the most no of times , then the second one then the 3rd one which apears only once

I was able to remove the duplicates but unable to arrange them — learner, May 13 '16 at 11:31
Give code example. and tell more accurate what do you need ( provide kind of result, that you need ) — xAqweRx, May 13 '16 at 11:31
What is "in order of their occurrence from most to least"? In what context? — Tim Visser, May 13 '16 at 11:37

score 0 · Answer 1 · answered May 13 '16 at 11:41

Of course there is a million different approaches, but a rather simple one would be to first count the occurrences of the different items and then sort the unique values based on that:

var input = [
    "57358e5dbd2f8b960aecfa8c",
    "573163a52abda310151e5791",
    "573163a52abda310151e5791",
    "573163a52abda310151e5791",
    "573163a52abda310151e5791",
    "573163da2abda310151e5792",
    "57358e5dbd2f8b960aecfa8c",
    "57358e5dbd2f8b960aecfa8c",
    "573163da2abda310151e5792"
];

var count = {};
input.forEach(function(item) {
    if(count.hasOwnProperty(item)) count[item]++;
    else count[item] = 1;
});

var output = Object.keys(count).sort(function(left, right) {
   if(count[left] < count[right]) return 1;
   if(count[left] > count[right]) return -1;
   return 0;
});

score 0 · Answer 2 · answered May 13 '16 at 11:50

You can make an array of key-value pairs (key, occurances), like this:

var arr = [];

for (var i = 0; i < myArray.length; i++) {
    if (arr.indexOf(myArray[i]) > -1) {
        // It occured before, search the key-value pair
        // and increment the occurance
        arr.indexOf(myArray[i])[1]++;
    } else {
        // Add to our array
        arr.push({myArray[i], 1});
    }
}

function compare(a, b) {
    if (a[1] < b[1]) return -1;
    else if (a[1] > b[1]) return 1;
    else return 0;
}

arr.sort(compare);

That way, you have total control over your sorting algorithm, and have the exact number of occurances as an added bonus! Hope this helps.

removing duplicate entries from an array and arranging in order in javascript

2 Answers2