javascript processing an array of objects to obtain a new array of objects

Question

I need to obtain from a given array of objects another array of objects but a little bit processed. Example:

 var arr =   [
      {
        "level": "INF",
        "model": "A"
      },{
        "level": "INF",
        "model": "B"
      },{
        "level": "INF",
        "model": "C"
      },{
        "level": "INC",
        "model": "A"
      },{
        "level": "IND",
        "model": "A"
      },{
        "level": "IND",
        "model": "B"
      }
]

process_array(arr)

should return:

      [{
        "level": "INF",
        "model": "A-B-C"
      },{
        "level": "INC",
        "model": "A"
      },{
        "level": "IND",
        "model": "A-D"
      }]

I mean, there only will be one object per different level and all the different models for that level will be concatenated by '-'.

What would be an easy way to achieve so?

My approach, for getting an array with different levels:

function process_array(array) {
    var values_seen = {}; // for removing duplicates
    for (var i = 0; i < array.length; i++) {
        values_seen[array[i]["level"]] = true;
    }
    return Object.keys(values_seen);
}

Now i need to obtain the concatented models for each levels..

You should add the code you've already tried to your question. — Andy
– Andy, Commented Apr 9, 2015 at 11:32

Ja͢ck · Accepted Answer · 2015-04-09 12:25:20Z

4

Just reduce the array into an object:

return array.reduce(function(total, current) {
  if (total[current.level]) { // existing
    total[current.level].model += '-' + current.model;
  } else { // new
    total[current.level] = current;
  }
  return total;
}, {});

Demo

In each iteration you modify the total object and then return it to be used within the next iteration. The final value of that object is returned to the caller.

1 Comment

Jeff Over a year ago

Smart! Didn't think of using reduce like that.

Vigneswaran Marimuthu · Accepted Answer · 2015-04-09 11:46:42Z

var arr =   [
      {
        "level": "INF",
        "model": "A"
      },{
        "level": "INF",
        "model": "B"
      },{
        "level": "INF",
        "model": "C"
      },{
        "level": "INC",
        "model": "A"
      },{
        "level": "IND",
        "model": "A"
      },{
        "level": "IND",
        "model": "B"
      }
]

function processArray(array) {
    
    var count = array.length, i, item, result = [], temp = {};
    
    for (i = 0; i < count; i++) {
        item = array[i];
      
        if (temp[item.level] !== undefined) {
            result[temp[item.level]].model += '-' + item.model;        
        } else {
            temp[item.level] = result.length;
            result.push(item);
        }
        
    }

    return result;
}

alert(JSON.stringify(processArray(arr)));

Jeff · Accepted Answer · 2015-04-09 11:53:09Z

What you are referring to is also called projection.

This code uses EcmaScript 5.

var arr =   [
      {
        "level": "INF",
        "model": "A"
      },{
        "level": "INF",
        "model": "B"
      },{
        "level": "INF",
        "model": "C"
      },{
        "level": "INC",
        "model": "A"
      },{
        "level": "IND",
        "model": "A"
      },{
        "level": "IND",
        "model": "B"
      }
];

function processArray(input) {
    var buf = {}, result = [];
    input.forEach(function(item) {
        var model = item.model;
        var existing = buf[item.level];
        if (existing) {
           existing.model += '-' + item.model;         
        } else {
            existing = buf[item.level] = {
                level: item.level,
                model: model
            };
            result.push(existing);
        }
    });
    return result;
}

var processed = processArray(arr);
console.log(processed);

gion_13 · Accepted Answer · 2015-04-09 11:54:05Z

function processArray(arr) {
    var result = [];
    arr
        .map(function(v) {return v.level;})
        .forEach(function(v, i) {
            var resultValue = result.filter(function(el, j) {
                return el.level === v;
            })[0];

            if(!resultValue) {
              result.push(arr[i]); 
            } else {
              resultValue.model += '-' + arr[i].model;
            }
        });
    return result;
}

var arr = [
      {
        "level": "INF",
        "model": "A"
      },{
        "level": "INF",
        "model": "B"
      },{
        "level": "INF",
        "model": "C"
      },{
        "level": "INC",
        "model": "A"
      },{
        "level": "IND",
        "model": "A"
      },{
        "level": "IND",
        "model": "B"
      }
];

alert(JSON.stringify(processArray(arr), null, 2));

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