Combine/merge objects in array based upon common v

Question

I have an array like the following.

[ { sku: 'TEA-BLCK', price: '10', quantity: '1' },
  { sku: 'TEA-ELGY', price: '10', quantity: '1' },
  { sku: 'TEA-CHAI', price: '10', quantity: '1' },
  { sku: 'TEA-GREN', price: '10', quantity: '1' },
  { sku: 'TEA-ELGY', price: '10', quantity: '1' },
  { sku: 'TEA-MINT', price: '10', quantity: '1' } ]

I need to make it look like this

[ { sku: 'TEA-BLCK', price: '10', quantity: '1' },
  { sku: 'TEA-ELGY', price: '10', quantity: '2' },
  { sku: 'TEA-CHAI', price: '10', quantity: '1' },
  { sku: 'TEA-GREN', price: '10', quantity: '1' },
  { sku: 'TEA-MINT', price: '10', quantity: '1' } ]

I got so far to make this reduce function using underscore.js.

var reduce = function(){
    return _.reduce(line_items, function(quant, item) {
        quant[item.sku] = (typeof(quant[item.sku]) !== "undefined") ? quant[item.sku] : 0 ;
        quant[item.sku] = parseFloat(item.quantity) + quant[item.sku];
        return quant;
    }, {});
}

Which spits out the following.

{ 'TEA-BLCK': 1,
  'TEA-ELGY': 1,
  'TEA-CHAI': 2,
  'TEA-GREN': 1,
  'TEA-MINT': 1 }

Is this a good job for reduce? How can I get it the way I want?

Answer 1

I was a bit late to the party, but it sounded so fun, so..

JSON.stringify(
[ { sku: 'TEA-BLCK', price: '10', quantity: '1' },
  { sku: 'TEA-ELGY', price: '10', quantity: '1' },
  { sku: 'TEA-CHAI', price: '10', quantity: '1' },
  { sku: 'TEA-GREN', price: '10', quantity: '1' },
  { sku: 'TEA-ELGY', price: '10', quantity: '1' },
  { sku: 'TEA-MINT', price: '10', quantity: '1' } ].sort( function (a, b) {
   return a.sku < b.sku;
} ).reduce( function (a,v) {
   if ( !a[0] || a[0].sku !== v.sku  ) {
      a.unshift(v);
   } else {
      // notice the very inefficient str -> number -> str conversion
      a[0].quantity = 1*a[0].quantity + 1*v.quantity + '';
   }

   return a;
 }, []) );

Here we pre-sort the array, and then add elements to the beginning of accumulator. And GGG have already said about strings.

http://jsfiddle.net/EqGUe/

Answer 2

Technically this is the complete answer. From string to string. Sorry guys.

var line_items = [
    { sku: 'TEA-BLCK', price: '10', quantity: "2" },
    { sku: 'TEA-ELGY', price: '10', quantity: "3" },
    { sku: 'TEA-CHAI', price: '10', quantity: "1" },
    { sku: 'TEA-GREN', price: '10', quantity: "1" },
    { sku: 'TEA-ELGY', price: '10', quantity: "1" },
    { sku: 'TEA-MINT', price: '10', quantity: "1" }
];

// Group items by sku.
var line_items_by_sku = _(line_items).groupBy(function (item) { return item.sku; });

// Get the new line_items array based on the grouped data.
line_items = _(line_items_by_sku).map(function (items) {
    var item = items[0];
    item.quantity = _.reduce(items, function(memo, item){ return memo + parseFloat(item.quantity); }, 0);
    item.quantity = item.quantity.toString();
    return item;
});

document.write("<pre>"+JSON.stringify(line_items, null, " ")+"</pre>");

Answer 3

What about a simple solution like this:

function reduce(array) {
    var out = [];
    var indexBySku = {};
    for (var i = array.length; i--;) {
        if (!indexBySku[array[i].sku]) {
            indexBySku[array[i].sku] = out.length;
            out.push(array[i]);
        } else {
            out[indexBySku[array[i].sku]].quantity -= -array[i].quantity;
        }
    }
    return out;
}

http://jsfiddle.net/waV6H/1

Probably the only thing that needs explanation here is the line where we subtract a negative instead of adding. This is just to avoid string concatenation, since the values in "quantity" are strings.

---

Super condensed version, dropping unneeded braces and semicolons... just for fun. Preserves order and quantity as string, works with quantity != 1.

function reduce(array) {
    var out = [], indexBySku = {}, len = array.length, i, j
    for (i = 0; i < len; i++)
        (j = indexBySku[array[i].sku]) ?  
            out[j].quantity = out[j].quantity - -array[i].quantity + '' :
            indexBySku[array[i].sku] = out.push(array[i]) - 1
    return out
}

Answer 4

Try something like this:

var line_items = [
    { sku: 'TEA-BLCK', price: '10', quantity: 2 },
    { sku: 'TEA-ELGY', price: '10', quantity: 3 },
    { sku: 'TEA-CHAI', price: '10', quantity: 1 },
    { sku: 'TEA-GREN', price: '10', quantity: 1 },
    { sku: 'TEA-ELGY', price: '10', quantity: 1 },
    { sku: 'TEA-MINT', price: '10', quantity: 1 }
];

// Group items by sku.
var line_items_by_sku = _(line_items).groupBy(function (item) { return item.sku; });

// Get the new line_items array based on the grouped data.
line_items = _(line_items_by_sku).map(function (items) {
    var item = items[0];
    item.quantity = _.reduce(items, function(memo, item){ return memo + item.quantity; }, 0);
    return item;
});

See this jsfiddle.

Answer 5

A bit late as well, but fun to work out http://jsbin.com/amazat/2/

line_items_reduced = _.map(reduce(), function(value, key) {
  var line_item = _.find(line_items, function(line_i){
    return (key === line_i.sku);
  });
  line_item.quantity = value;
  return line_item;
});

Answer 6

This updates benekastah's answer and handles quantities more than 1... But I did take the liberty to change quantity to an integer

http://jsfiddle.net/xjUDY/3/

var line_items = [
    { sku: 'TEA-BLCK', price: '10', quantity: 2 },
    { sku: 'TEA-ELGY', price: '10', quantity: 3 },
    { sku: 'TEA-CHAI', price: '10', quantity: 1 },
    { sku: 'TEA-GREN', price: '10', quantity: 1 },
    { sku: 'TEA-ELGY', price: '10', quantity: 1 },
    { sku: 'TEA-MINT', price: '10', quantity: 1 }
];

// Group items by sku.
var line_items_by_sku = _(line_items).groupBy(function (item) { return item.sku; });

// Get the new line_items array based on the grouped data.
line_items = _(line_items_by_sku).map(function (items) {
    var item = items[0];
    item.quantity = _.reduce(items, function(memo, item){ return memo + item.quantity; }, 0);
    return item;
});

document.write("<pre>"+JSON.stringify(line_items, null, " ")+"</pre>");
​