Create totals array from two-dimensional array in Javascript

Question

Say I have this two-dimensional array:

// [name, item, price]

var arr = [
    ['bob', 'book', '3'],
    ['mary', 'pencil', '2'],
    ['steve', 'book', '2'],
    ['steve', 'pencil', '1'],
    ['bob', 'book', '2']
];

I need to create a second array which contains:

each name only once
a total for each name
an array of objects, each object representing an item and corresponding price.

For instance:

// [name, total_price, [ { item: item, price: price } ] ] 

totals = [
    ['bob', 5, [ { item: 'book', price: 3 }, { item: 'book', price: 2 } ] ],
    ['mary', 2, [ { item: 'pencil', price: 2 } ] ],
    ['steve', 3, [ { item: 'book', price: 2 }, { item: 'pencil', price: 1 } ] ] 
];

What is the best way to create that totals array?

Also, the array of objects with the items and prices could even just be a two-dimensional array if that's more efficient, like this:

// [name, total_price, [ [item, price], [item, price], [item, price] ] ]

So you basically want us to do your work for you?

dangor
– dangor

2015-08-16 20:07:36 +00:00
Commented Aug 16, 2015 at 20:07 — dangor
– dangor, Commented Aug 16, 2015 at 20:07

dfsq · Accepted Answer · 2015-08-16 20:21:00Z

1

You can use Array.prototype.reduce. For example with help of temporary map variable to store array indexes:

var arr = [
    ['bob', 'book', '3'],
    ['mary', 'pencil', '2'],
    ['steve', 'book', '2'],
    ['steve', 'pencil', '1'],
    ['bob', 'book', '2']
];

var names = {};
var result = arr.reduce(function(prev, curr) { 
    if (names[curr[0]] === undefined) {
        prev.push([curr[0], 0, []]);
        names[curr[0]] = prev.length - 1;
    }
    var i = names[curr[0]];
    prev[i][1] += Number(curr[2]);
    prev[i][2].push({item: curr[1], price: curr[2]});
    return prev;
}, []);

document.write('<pre>' + JSON.stringify(result, null, 4));

answered Aug 16, 2015 at 20:21

dfsq

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Repo · Accepted Answer · 2015-08-16 21:01:46Z

There you go =)

var arr = [
  ['bob', 'book', '3'],
  ['mary', 'pencil', '2'],
  ['steve', 'book', '2'],
  ['steve', 'pencil', '1'],
  ['bob', 'book', '2']
];

totals = [];



$(document).ready(function() {

  console.log(arr);
  console.log(totals);
  
  $.each(arr, function(i, order) {
    var inserted = false;

    $.each(totals, function(j, totalsOrder) {
      if (order[0] == totalsOrder[0]) {
        totalsOrder[1] = totalsOrder[1] + parseInt(order[2]);
        var item = {
          item: order[1],
          price: parseInt(order[2])
        };
        totalsOrder[2].push(item);
        inserted = true;
      }
    });
    if (!inserted) {
      var totalsItem = [order[0], parseInt(order[2]),
        [{
          item: order[1],
          price: parseInt(order[2])
        }]
      ];
      totals.push(totalsItem);
    }

  });
  console.log(totals);

});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

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