Removing duplicate key value pair in javascript array - Stack Overflow

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I have a javascript array which get created dynamically in this format.

[{prdName: "Testing2"},
{prdName: "Testing2,Testing3"},
{markets: "Testing5"},
{markets: "Testing5,Testing6"}]

I want to remove the duplicate key in the above array map and convert it into this format.

 [ {prdName: "Testing2,Testing3"},
   {markets: "Testing5,Testing6"} ]

Could you let me know how to achieve the same. I am working on a reactjs application.

I have a javascript array which get created dynamically in this format.

[{prdName: "Testing2"},
{prdName: "Testing2,Testing3"},
{markets: "Testing5"},
{markets: "Testing5,Testing6"}]

I want to remove the duplicate key in the above array map and convert it into this format.

 [ {prdName: "Testing2,Testing3"},
   {markets: "Testing5,Testing6"} ]

Could you let me know how to achieve the same. I am working on a reactjs application.

• javascript

Share Improve this question Follow edited Oct 27, 2017 at 18:52 Daniel Beck 21.5k55 gold badges4343 silver badges6060 bronze badges asked Oct 27, 2017 at 18:48 Rakesh NallamRakesh Nallam 29322 gold badges66 silver badges1818 bronze badges 2

• 1 Does the filtering have to be aware of the values inside the strings? For example, if the array is [{a:"Test1"}, {a:"Test2"}] the result must be [{a:"Test1,Test2"}] or it's enough to just get the latest ocurrence of "a" (resulting in [{a:"Test2"}])? – Raphael Commented Oct 27, 2017 at 18:57
• Does the output really need to be an array? It looks like you could just merge all of the objects into one, and it would remove duplicate keys. – castletheperson Commented Oct 27, 2017 at 19:00

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3 Answers 3

Sorted by: Reset to default 3

With ES6, you could use Map with Set for unique items.

var array = [{ prdName: "Testing2" }, { prdName: "Testing2,Testing3" }, { markets: "Testing5" }, { markets: "Testing5,Testing6" }],
    map = new Map,
    result;

array.forEach(o => Object.keys(o).forEach(k => {
    if (!map.has(k)) {
        map.set(k, new Set);
    }
    o[k].split(',').forEach(s => map.get(k).add(s));
}));

result = [...map].map(([k, s]) => ({ [k]: [...s].join() }));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

I'm assuming that you want to preserve all of the non-duplicate ma-delimited entries, not just throw away all but the last group as in the other answers. (So, for example, if the input were [{foo: "x"}, {foo:"x,y"}, {foo:"z"}] the output should be [{foo: "x,y,z"}], not [{foo:"z"}].)

var rearrange = function(input) {
  var tmp = {}; // track keys and values as we find them
  for (obj of input) {
    var key = Object.keys(obj)[0]; // each input has one key
    tmp[key] = tmp[key] || {}; // initialize an empty object at that key in tmp if necessary
    var vals = obj[key].split(",");
    for (v of vals) {
      tmp[key][v.trim()] = 1; // keep each of the (trimmed) ma-delimited values, implicitly dropping duplicates
    }
  }

  // now convert the tmp object into an array:
  var output = [];
  for (k of Object.keys(tmp)) {
    var x = {};
    x[k] = Object.keys(tmp[k]).join(","); // merge the values back into a ma-separated string
    output.push(x);
  }
  return output;
}
console.log(rearrange([
  {prdName: "Testing2"},
  {prdName: "Testing2,Testing3"},
  {markets: "Testing5"},
  {markets: "Testing5,Testing6"}
]));

console.log(rearrange([
  {foo: "x"},
  {foo: "x,y"},
  {foo: "z"},
  {bar: "x,y,z"}
]));

If, however, all you need is the last instance of each key, this is pretty close to a one-liner; just use Object.assign to merge the objects:

var rearrange = function(input) {
   var merged = Object.assign({},...input); // merges all input keys, overwriting early values with later ones
   
   // convert to array (if necessary. the "merged" object might be easier to work with...):
   var output=[];
   for (k of Object.keys(merged)) {
     var x = {};
     x[k] = merged[k];
     output.push(x)
   }
   return output;
}

console.log(rearrange([
    {prdName: "Testing2"},
    {prdName: "Testing2,Testing3"},
    {markets: "Testing5"},
    {markets: "Testing5,Testing6"}
]));
     
console.log(rearrange([{foo: "x"}, {foo:"x,y"}, {foo:"z"}]));

var lists =[{prdName: "Testing2"},

{prdName: "Testing2,Testing3"},

{markets: "Testing5"},

{markets: "Testing5,Testing6"}]

var newLists =[]
var keys = []
lists.forEach(item=>{
var key = Object.keys(item)[0];
if(keys.indexOf(key) === -1){
// first time the key is processed; it is stored in newLists
    keys.push(key);
    newLists.push(item);
  }
else {
// a duplicate key is found in the array
    let remove; 
    let values;
    newLists.forEach((item2,index) => {
        if (Object.keys(item2)[0] === key) {
// use of a set to have a union of values already stored for the key and the new values found for the same key using spread operator        
         values = new Set([...item2[key].split(","),...item[key].split(",")]);
            remove = index;
          }
    })
    newLists.splice(remove, 1);
    newLists.push({[key]:  Array.from(values).toString()})
  }
})

console.log(newLists);

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