Merging two Multidimensional Arrays into a Multidimensional Array with Objects

Question

I'm learning the new JavaScript ES6 syntax and am trying to create a multidimensional array with objects from 2 other multidimensional arrays. Presumably my syntax is incorrect, but I don't know how to fix it. The result should be:

[
  [{    letter: w,    instances: 1
  }, {  letter: o,    instances: 1
  }, {  letter: d,    instances: 2
  }, {  letter: r,    instances: 1
  }],
  [{    letter: s,    instances: 1
  }, {  letter: y,    instances: 1
  }],
  [{    letter: h,    instances: 1
  }, {  letter: e,    instances: 1
  }, {  letter: l,    instances: 2
  }, {  letter: o,    instances: 1
  }]
]

My code uses two map methods:

var letters = [
  ["w", "o", "d", "r"],
  ["s", "y"],
  ["h", "e", "l", "o"]
];
var numbers = [
  [1, 1, 2, 1],
  [1, 1][1, 1, 2, 1]
];
var objArr = letters.map(function(c, i) {
  return c.map(function(c2, i2, a2) {
    return {
      letter: c2,
      instances: numbers[i]
    }
  })
});
console.log(objArr);

It correctly returns a multidimensional array with objects and correct letter values, but the number values are incorrect. Can anyone find why this happens? Also, does anyone think there's a better way of storing the letters and the number of numbers?

Nitish Narang · Accepted Answer · 2018-11-14 12:21:24Z

3

One very small mistake in instances: Pls see below

var letters = [["w", "o", "d", "r"],["s", "y"],["h", "e", "l", "o"]];

var numbers = [[1,1,2,1],[1,1], [1,1,2,1]];

var objArr = letters.map(function(c,i) {
                return c.map(function(c2,i2) {
                    return {letter: c2, instances: numbers[i][i2]}
                })
            });

console.log(objArr)

answered Nov 14, 2018 at 12:21

Nitish Narang

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Comments

Hassan Imam · Accepted Answer · 2018-11-14 12:32:01Z

1

Since you have a two-dimensional array, you need to use two indexes to access it. Use the first index i, to access the inner array and the use second index j, to access the number inside the array.

let letters = [["w", "o", "d", "r"],["s", "y"],["h", "e", "l", "o"]],
    numbers = [[1, 1, 2, 1],[1, 1],[1, 1, 2, 1]],
    result = letters.map((arr, i) => arr.map((letter, j) => ({letter,instances: numbers[i][j]})));
console.log(result);

answered Nov 14, 2018 at 12:32

Hassan Imam

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2 Comments

user8758206 Over a year ago

one thing I don't understand is this part: {letter,instances: numbers[i][j]} - why wouldn't it be {letter: letter,instances: numbers[i][j]}? how does your code know to assign letter as 'letter'?

Hassan Imam Over a year ago

It's object shorthand property names introduced in ES2015.

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