flagging duplicates in an array

Question

After requesting some user pictures, I end up with an array like this:

[
    { label: "portrait", owner: "Jon" },
    { label: "house", owner: "Jim" },
    { label: "portrait", owner: "Jim" },
    { label: "portrait", owner: "Jane" },
    { label: "cat", owner: "Jane" }
]

I need to highlight items whose label occurs multiple times in the array (here: "portrait").

Ideally, there'd be one flag (A) for items whose label occurs again later in the array, and another flag (B) for the final occurrence (i.e. both Jon's and Jim's portraits are flagged A, while Jane's gets B).

Any help would be greatly appreciated!

Answer 1

I'm not sure what you're trying to do, but maybe you just need to aggregate the data?

var data = [
    { name: "portrait", owner: "Jon" },
    { name: "house", owner: "Jim" },
    { name: "portrait", owner: "Jim" },
    { name: "portrait", owner: "Jane" },
    { name: "cat", owner: "Jane" }
];

var byName = {};

for (var i = 0, l = data.length; i < l; ++i) {
    if (!byName[data[i].name]){
        byName[data[i].name] = [];
    }
    byName[data[i].name].push(data[i].owner);
}

// byName == {portrait: ["Jon", "Jim", "Jane"], house: ["Jim"], cat: ["Jane"]}

var byOwner = {};

for (var i = 0, l = data.length; i < l; ++i) {
    if (!byOwner[data[i].owner]) {
        byOwner[data[i].owner] = [];
    }
    byOwner[data[i].owner].push(data[i].name);
}

---

Or maybe you like this better:

var data = [
    { name: "portrait", owner: "Jon" },
    { name: "house", owner: "Jim" },
    { name: "portrait", owner: "Jim" },
    { name: "portrait", owner: "Jane" },
    { name: "cat", owner: "Jane" }
];

var byName = [];

for (var i = 0, l = data.length; i < l; ++i) {
    var done = false;
    for (var j = 0, k = data.length; j < k; ++j) {
        if (byName[j] && byName[j].name == data[i].name) {
            byName[j].data.push(data[i].owner);
            done = true;
        }
    }
    if (!done) {
        byName.push({name: data[i].name, data: [data[i].owner]});
    }
}

/*
byName == [
    {name: "portrait", data: ["Jon", "Jim", "Jane"]},
    {name: "house", data: ["Jim"]},
    {name: "cat", data: ["Jane"]}
] */

Because posting random code is fun and you know it!

Answer 2

I'd suggest looping through the picture array and adding a flagged member to each object, depending if it's duplicate. See below for an example. It will assign anything with a duplicate with an 'A' and the last duplicate with a 'B'. Anything that is not a duplicate is not flagged.

var picture_array = [
        {label: 'portrait', owner: "Jon"},
        {label: 'house', owner: "Jim"},
        {label: 'portrait', owner: "Jim"},
        {label: 'portrait', owner: "Jane"},
        {label: 'cat', owner: "Jane"}
    ],
    length = picture_array.length;

//Loop through picture_array

for(var i = 0; i < length; i++) {
    var picture = picture_array[i],
        label = picture.label;

    //If picture has already been flagged, go the the next picture
    if (picture.flagged) {
       continue;
    }

    //Loop through rest of the array to compare duplicate labels
    var picture_a = picture;
    for(var j = i + 1; j < length; j++) {
        var picture_b = picture_array[j];

        //If picture_a matches picture_b then flag both of them appropriately
        if (picture_a.label == picture_b.label) {
            picture_a.flagged = 'A';
            picture_b.flagged = 'B';
            picture_a = picture_b;
        }
    }
}