Javascript - Reduce array with multiple-key objects [duplicate]

Question

I want to modify a Javascript array, so that the elements having the same values for specifies properties merge into one object in a way that the other properties are kept as a comma-separated string, JSON string, or an array. Basically, I want to turn this:

[
    {
        "language" : "english",
        "type" : "a",
        "value" : "value1"
    },
    {
        "language" : "english",
        "type" : "a",
        "value" : "value2"
    },
    {
        "language" : "english",
        "type" : "b",
        "value" : "value3"
    },  
    {
        "language" : "spanish",
        "type" : "a",
        "value" : "valor1"
    }
]

into this:

[
    {
        "language" : "english",
        "type" : "a",
        "value" : ["value1" , "value2"]  // A Json string is welcome too
    },
    {
        "language" : "english",
        "type" : "b",
        "value" : "value3"
    },  
    {
        "language" : "spanish",
        "type" : "a",
        "value" : "valor1"
    }
]

I have tried iterating and filtering, then upserted the object as given in the snippet. But I wonder if there is a more elegant way to do that.

P.S EcmaScript6 and additional JS library suggestions are also welcome.

var originalArray = [
	{
		"language" : "english",
		"type" : "a",
		"value" : "value1"
	},
	{
		"language" : "english",
		"type" : "a",
		"value" : "value2"
	},
	{
		"language" : "english",
		"type" : "b",
		"value" : "value3"
	},	
	{
		"language" : "spanish",
		"type" : "a",
		"value" : "valor1"
	}
];

var resultingArray = [];

// iterate through the original array
$.each(originalArray, function(i, val) {
  // apply filter on key properties (i.e. language and type)
  var result = resultingArray.filter(function( obj ) {
    return (obj.language === val.language && obj.type === val.type);
  });
  // if a record exists, update its value
  if (result.length === 1) {  
    result[0].value += (", " + val.value);
  } 
  // else, add value
  else if (result.length === 0) {
    resultingArray.push(val);
  }
  // if multiple rows exist with same key property values...
  else {
    alert("Too many records with language '" + val.language + "' and type '" + val.type + "'");
  }
});

console.log(JSON.stringify(resultingArray));

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

Here was my suggested solution, depending on what you consider "elegant". The trouble with your code is it runs in O(N^2), since the filter function runs once on the first iteration of each, twice, on the second iteration, and so on. There's no need for that. — A. Vidor
– A. Vidor, Commented Jul 27, 2016 at 9:57
And here was mine, where value is always an array. BTW: I think your alert() statement can never be triggered. If you don't want twice the same value for the same key (language + type), you'll have to do it differently. — Arnauld
– Arnauld, Commented Jul 27, 2016 at 10:04
hey, your JS was using jQuery, why you don't add jQuery tag? I was learn and make sure using pure javascript forEach to help you -_-! — Fadhly Permata
– Fadhly Permata, Commented Jul 27, 2016 at 10:12
Incidentally, I'm not sure it can be seen an exact duplicate of the suggested question as the OP is using a composite key, making the existing answers inadequate. — Arnauld
– Arnauld, Commented Jul 27, 2016 at 10:18
@Arnauld I'm not sure adding a secondary check warrants an entirely new question. The answers given are entirely appropriate, they just require a small modification. — CodingIntrigue
– CodingIntrigue, Commented Jul 27, 2016 at 11:07

Fadhly Permata · Accepted Answer · 2016-07-27 10:10:48Z

This is what you need?

var baseData= [
    {
        "language"  : "english",
        "type" : "a",
        "value" : "value1"
    },
    {
        "language" : "english",
        "type" : "a",
        "value" : "value2"
    },
    {
        "language" : "english",
        "type" : "b",
        "value" : "value3"
    },  
    {
        "language" : "spanish",
        "type" : "a",
        "value" : "valor1"
    }
];

var newData = [];
baseData.forEach(function(item, index) {
  if (newData.length === 0) {
    newData.push(item);
    
  } else {
    var dIndex = -1;
    newData.forEach(function(itm, idx) {
      if (item.language === itm.language && item.type === itm.type) dIndex = idx;
    });
    
    if (dIndex !== -1) {
      var oldValue = newData[dIndex].value;
      
      if (typeof(oldValue).toString() === 'string') {
        newData[dIndex].value = [oldValue, item.value];
      }
    } else {
      newData.push(item);
    }
  }
});
console.log(newData);

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