javascript - How to dynamically set the key in a reduce function - Stack Overflow

I have a .txt file with all the scrabble letter quantities in:

A-9, B-2, C-2, D-4, E-12, F-2, G-3, H-2, I-9, J-1, K-1, L-4, M-2, N-6, O-8, P-2, Q-1, R-6, S-4, T-6, U-4, V-2, W-2, X-1, Y-2, Z-1

I am trying to get an array of objects from this, where the key is the letter, and the value is the number.

The problem I am having is where I am trying to set the key to be the first item in the array (that I split earlier) [A, 9].

The code I have is as follows. Any tips would be gratefully received :)

import fs from 'fs'

var output = fs.readFileSync('scrabble-quantities.txt', 'utf-8')
    .trim()
    .split(', ')
    .map(item => item.split('-'))
    .reduce((quantities, item) => {
        quantities.push({
            item[0]: item[1]
        })
        return quantities
    }, [])    

Thanks

I have a .txt file with all the scrabble letter quantities in:

A-9, B-2, C-2, D-4, E-12, F-2, G-3, H-2, I-9, J-1, K-1, L-4, M-2, N-6, O-8, P-2, Q-1, R-6, S-4, T-6, U-4, V-2, W-2, X-1, Y-2, Z-1

I am trying to get an array of objects from this, where the key is the letter, and the value is the number.

The problem I am having is where I am trying to set the key to be the first item in the array (that I split earlier) [A, 9].

The code I have is as follows. Any tips would be gratefully received :)

import fs from 'fs'

var output = fs.readFileSync('scrabble-quantities.txt', 'utf-8')
    .trim()
    .split(', ')
    .map(item => item.split('-'))
    .reduce((quantities, item) => {
        quantities.push({
            item[0]: item[1]
        })
        return quantities
    }, [])    

Thanks

• javascript

Share Improve this question Follow edited Feb 16, 2016 at 11:49 zeKoko asked Feb 15, 2016 at 16:39 zeKokozeKoko 43711 gold badge77 silver badges1919 bronze badges 1

• What do you want the resulting array to be? – T.J. Crowder Commented Feb 15, 2016 at 16:43

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 6

I would use an object instead of an array. It's easier and more natural how JS works:

// ...
.reduce((quantities, item) => {
    quantities[item[0]] = item[1];
    return quantities;
}, {});

The resulting output object is then (in JSON notation):

{
  "A": 9,
  "B": 2,
  // ...
  "Z": 1
}

EDIT: mind the value type

If you want the value to be an actual number you will have to parse it in the assignment with:

parseInt(item[1], 10)

To create a key (property name) dynamically, you need to do one of two things:

1. In ES5 and earlier, you have to create the object and then set the property:

      var o = {};
      o[item[0]] = item[1];
   

2. In ES2015 (aka ES6) and later, you can use a dynamic property name in a property initializer via []:

      // ES2015 (ES6) ONLY
      quantities.push({
          [item[0]]: item[1]
      })
   

---

That said, I'd e at the problem differently, using regex and ending up with an object keyed by the letter rather than an array of objects:

var str = "A-9, B-2, C-2, D-4, E-12, F-2, G-3, H-2, I-9, J-1, K-1, L-4, M-2, N-6, O-8, P-2, Q-1, R-6, S-4, T-6, U-4, V-2, W-2, X-1, Y-2, Z-1";
var quantities = {};
str.match(/[A-Z]-\d/g).forEach(function(entry) {
  quantities[entry.charAt(0)] = +entry.replace(/.-/, '');
});
console.log(quantities);

Then, looking up the quantity of a letter bees quantities.A (or quantities[letter] if letter is a variable containing "A"):

console.log(quantities.A); // 9