Splitting an array of arrays

Question

I have an array of arrays that looks like this.

const data = [
    ['list1'],
    ['item1', '1'],
    ['item2', '2'],
    ['item3', '3'],
    ['item4', '4'],
    [' ']
    ['list2'],
    ['item1', '1'],
    ['item2', '2'],
    ['item3', '3'],
    ['item4', '4'],
    [' ']
    ['list3'],
    ['item1', '1'],
    ['item2', '2'],
    ['item3', '3'],
    ['item4', '4'],
    [' ']
]

I need to get all of the items between the list1, list2 & list3 and the empty value to build a more structured container so that list1, list2 & list3 include the items as children. e.g. {

const data2 = {
    'list1': {'item1': '1', 'item2': '2', 'item3': '3', 'item4': '4'},
    'list2': {'item1': '1', 'item2': '2', 'item3': '3', 'item4': '4'},
    'list3': {'item1': '1', 'item2': '2', 'item3': '3', 'item4': '4'},
    'list4': {'item1': '1', 'item2': '2', 'item3': '3', 'item4': '4'}
}

Whats the most efficient way to query the data array to get the items between the list headers? I see lodash has a _.slice method which takes an index but I can't see a way to use the value of the array as a delimiter.

Xiaoy312 · Accepted Answer · 2017-10-10 21:07:50Z

2

Try this:

const data = [
  ['list1'],
  ['item1', '1'],
  ['item2', '2'],
  ['item3', '3'],
  ['item4', '4'],
  [' '],
  ['list2'],
  ['item1', '1'],
  ['item2', '2'],
  ['item3', '3'],
  ['item4', '4'],
  [' '],
  ['list3'],
  ['item1', '1'],
  ['item2', '2'],
  ['item3', '3'],
  ['item4', '4'],
  [' ']
];

var result = {};
var lastList = null;
for (var item of data) {
  if (item.length == 1 && item[0] != ' ') {
    result[item[0]] = lastList = {};
  }

  else if (lastList != null && item.length == 2) {
    lastList[item[0]] = item[1];
  }
}

console.log(result);

edited Oct 10, 2017 at 21:07

answered Oct 10, 2017 at 20:53

Xiaoy312

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4 Comments

styfle Over a year ago

Should the second if be else if?

user1513388 Over a year ago

Yep this does the trick. Its certainly more understandable than the previous answer. The only issues is that my list names and item names will likely be different. i.e. they won't start with 'list' and 'item'

Xiaoy312 Over a year ago

@user1513388 Does the edited solution work? If not, show us your real data, or describe it.

styfle Over a year ago

Change == to be ===

Nina Scholz · Accepted Answer · 2017-10-10 20:43:31Z

2

You could reduce the whole array by using a closure over a reference to the last object with the given key.

var data = [['list1'], ['item1', '1'], ['item2', '2'], ['item3', '3'], ['item4', '4'], [' '], ['list2'], ['item1', '1'], ['item2', '2'], ['item3', '3'], ['item4', '4'], [' '], ['list3'], ['item1', '1'], ['item2', '2'], ['item3', '3'], ['item4', '4'], [' ']],
    result = data.reduce(function (ref) {
        return function (r, a) {
            if (1 in a) {
                ref[a[0]] = a[1];
            } else if (a[0].trim()) {
                r[a[0]] = {};
                ref = r[a[0]]
            }
            return r;
        };
    }(undefined), {});

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Oct 10, 2017 at 20:43

Nina Scholz

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3 Comments

user1513388 Over a year ago

I get a type error TypeError: Cannot use 'in' operator to search for '1' in undefined on the if (1 in a) line if I try this.

Nina Scholz Over a year ago

@user1513388, it works even in IE11, where do you get the error from?

user1513388 Over a year ago

I'm using nodeJS

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