Javascript array not creating an array

Question

I have an array with items and I want to group them according the first letter but when I push the item to the array it shows empty "Array[0]" while there are clearly items in it.

Apparently I'm doing something wrong but i have no idea what.

var group = [];
var alphabetArray = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
alphabetArray.forEach(function(letter) {
  group[letter] = group[letter] || [];
  group[letter].push({
    key: letter,
    letter
  });
});
console.log(group);

"group them according the first letter" - what do you mean? some kind of sort? — Vasily Liaskovsky
– Vasily Liaskovsky, Commented Jan 7, 2017 at 9:05
Please provide an expected result for input string AB, just for first two characters. I still have no idea what exactly are you looking for. — Vasily Liaskovsky
– Vasily Liaskovsky, Commented Jan 7, 2017 at 9:17

Quentin · Accepted Answer · 2017-01-07 09:03:26Z

2

Arrays are designed to hold an ordered set of data represented by property names which are integers.

You are assigning property names which are letters.

Arrays are not designed to hold that kind of data and console.log doesn't display those properties for arrays.

Don't use an array. Use an object. Objects are designed to hold unordered data with arbitrary property names. If order matters, then you might want to use a Map instead.

answered Jan 7, 2017 at 9:03

Quentin

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1 Comment

T.J. Crowder Over a year ago

Well, the names aren't integers (in that they're not numbers), but close enough. They're strings consisting of a series of digits denoting an integer in canonical format whose numeric value i is in the range +0 ≤ i < 2^32-1. :-)

mplungjan · Accepted Answer · 2017-01-07 09:04:13Z

1

You are looking to create an object instead of an array. Change the [] to {}

An Array expects an int as index, the object can take a string

var group = {}; // Object instead of Array
var alphabetArray = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
alphabetArray.forEach(function(letter) {
  group[letter] = group[letter] || [];
  group[letter].push({
    key: letter,
    letter
  });
});
console.log(group);

answered Jan 7, 2017 at 9:04

mplungjan

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2 Comments

Sephen Over a year ago

That works up to the point when i want to iterate through it in Angular 2 with ngFor

Vasily Liaskovsky Over a year ago

You really should mention that in question, that's XY-problem

Vasily Liaskovsky · Accepted Answer · 2017-01-07 09:25:26Z

0

I guess you want to transform each letter to structure. I f so, you need Array.map:

var alphabetArray = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
var group = alphabetArray.map(function(letter) {
  return {
    [letter]: letter
  };
});
console.log(group);

edited Jan 7, 2017 at 9:25

answered Jan 7, 2017 at 9:10

Vasily Liaskovsky

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