Combine/merge objects in array based upon common value

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?

reduce is not well suitable for this task. Consider starting with groupBy and then map. — user166390
– user166390, Commented Jan 4, 2013 at 20:18

benekastah · Accepted Answer · 2013-01-05 16:56:33Z

3

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.

edited Jan 5, 2013 at 16:56

answered Jan 4, 2013 at 20:21

benekastah

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1 Comment

benekastah Over a year ago

Very true. The updated jsfiddle already had it fixed, so I replaced with that. Thanks!

Dagg Nabbit · Accepted Answer · 2013-01-04 22:08:47Z

2

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
}

edited Jan 4, 2013 at 22:08

answered Jan 4, 2013 at 20:21

Dagg Nabbit

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2 Comments

benekastah Over a year ago

This solution is missing the item with sku TEA-BLCK.

Dagg Nabbit Over a year ago

@ThomasReggi no problem, thought you might like a plain vanilla solution :)

c69 · Accepted Answer · 2013-01-04 20:39:30Z

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/

answered Jan 4, 2013 at 20:39

c69

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3 Comments

Dagg Nabbit Over a year ago

Nice... functional, no dependencies, meets all requirements, works for quantities other than 1, preserves quantities as strings. ES5-only, though. +1

c69 Over a year ago

@GGG yes, but with es5shim you can give reduce even to IE6.

Dagg Nabbit Over a year ago

I don't think IE has Array#reduce until like 9... so maybe dependencies after all ;)

Nate- · Accepted Answer · 2013-01-04 21:24:52Z

1

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;
});

answered Jan 4, 2013 at 21:24

Nate-

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Nate- · Accepted Answer · 2013-01-04 22:01:31Z

1

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>");

answered Jan 4, 2013 at 22:01

Nate-

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1 Comment

ThomasReggi Over a year ago

Even though in my code there could never be more then one quantity. I prefer this.

ThomasReggi · Accepted Answer · 2013-01-04 22:19:37Z

0

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>");

answered Jan 4, 2013 at 22:19

ThomasReggi

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1 Comment

Dagg Nabbit Over a year ago

Why all that parseFloat / toString stuff and not just return memo - -item.quantity + '';

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