How to merge arrays in javascript in a different way?

Question

I want to merge arrays a little bit different way. I have 2 or more arrays like:

var array1 = ["apple", "banana"];

var array2 = ["apple", "apple", "orange"];

I want the output:

var array3 = ["apple", "apple", "banana", "orange"];

So if any given array has a variable in it more than once, merge algorithm should keep all of them from that array.

I saw some code that prevents duplication but it gives outputs like this:

var array3 = ["apple", "banana", "orange"];

for more example:

var arr1 = [1,2,3,4];

var arr2 = [1,1,2,4,5,5,5];

var arr3 = [1,3,3,5,5];

I want the output:

var array4 = [1,1,2,3,3,4,5,5,5];

How can I do this?

Answer 1

Here's one way to do it by counting the occurrences of each item in each array:

var arr1 = [1,2,3,4];
var arr2 = [1,1,2,4,5,5,5];
var arr3 = [1,3,3,5,5];

function joinCommon(/* list of arrays */) {
    var arr, arrayCounts, masterList = {}, item, output;
    // for each array passed in
    for (var i = 0; i < arguments.length; i++) {
        arr = arguments[i];
        arrayCounts = {};
        // iterate each array
        for (var j = 0; j < arr.length; j++) {
            item = arr[j];
            if (!arrayCounts[item]) {
                arrayCounts[item] = 1;
            } else {
                ++arrayCounts[item];
            }
            // now keep master list and master counts
            if (!masterList[item]) {
                masterList[item] = {cnt: 1, val: item};
            } else {
                masterList[item].cnt = Math.max(masterList[item].cnt, arrayCounts[item]);
            }
        }
    }
    // now output result
    output = [];
    for (var i in masterList) {
        for (var j = 0; j < masterList[i].cnt; j++) {
            output.push(masterList[i].val);
        }
    }
    return output;    
}

var results = joinCommon(arr1, arr2, arr3);

Working demo: http://jsfiddle.net/jfriend00/dtn6zw4m/