ES6 Processing Objects (Reduce Functions)

Question

Greetings from Romania,

Given a list of games, which are objects that look like:

  {
    "id": 112814,
    "matches": "123",
    "tries": "11"
  }

return a object like such

  {
    "totalMatches": m,
    "totalTries": y
  }

Where m is the sum of all matches for all games and t is the sum of all tries for all games.

 input = [
    {"id": 1,"matches": "123","tries": "11"},
    {"id": 2,"matches": "1","tries": "1"},
    {"id": 3,"matches": "2","tries": "5"}
  ]

  output = {
    matches: 126,
    tries: 17
  }

What I currently have:

function countStats(list) {


  return {
    matches: 0,
    tries: 0
  };
}

What I think I need to do:

Iterate through all objects
Use global variable to count matches (m) and tries (y)
Return m, y respectively

What I was told to do instead, which I do not know how: 1. Use the reduce function 2. Return an object instead

Many thanks for any advice

Jeto · Accepted Answer · 2018-10-12 09:20:17Z

2

You can make use of Array.reduce:

const input = [
  {"id": 1, "matches": "123", "tries": "11"},
  {"id": 2, "matches": "1", "tries": "1"},
  {"id": 3, "matches": "2", "tries": "5"}
];
  
const result = input.reduce((result, entry) => {
  result.matches += +entry.matches;
  result.tries += +entry.tries;
  return result;
}, {matches: 0, tries: 0});

console.log(result);

edited Oct 12, 2018 at 9:20

answered Oct 12, 2018 at 9:11

Jeto

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Comments

vahdet · Accepted Answer · 2018-10-12 09:12:47Z

1

You should use reduce on fields as such:

function countStats (list) {
  return {
    matches: input.reduce((a, b) => +a + +b.matches, 0),
    tries: input.reduce((a, b) => +a + +b.tries, 0)
  }
}

See the syntactic sugar to sum strings as numbers i.e. +a + +b

answered Oct 12, 2018 at 9:12

vahdet

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2 Comments

SpamFatFree Over a year ago

Thanks this is the format I had in mind. Can you please break down what the parameters a, b refer to? And what the ending 0 is?

vahdet Over a year ago

a and b are variables for that inline, anonymous function. Their names are arbitrary indeed. And the zeroes are the offset values representing the case that the initial value of our operation (sum) is zero. It can be omitted generally, however for this specific case, it is required as otherwise we would start off with a string which would mess up the result.

Nina Scholz · Accepted Answer · 2018-10-12 09:25:23Z

0

You could take an object for the result with zero values and take the keys for later iterating the array and the keys for adding same key values.

var input = [{ id: 1, matches: "123", tries: "11" }, { id: 2, matches: "1", tries: "1" }, { id: 3, matches: "2", tries: "5" }],
    output = { matches: 0, tries: 0 },
    keys = Object.keys(output);

input.forEach(o => keys.forEach(k => output[k] += +o[k]));

console.log(output);

answered Oct 12, 2018 at 9:25

Nina Scholz

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Comments

Lafi · Accepted Answer · 2018-10-12 10:22:41Z

0

here is a clean way of doing it:

const games = [
  { id: 1, matches: '123', tries: '11' },
  { id: 2, matches: '1', tries: '1' },
  { id: 3, matches: '2', tries: '5' },
];

const reduced = games.reduce(
  (accumulator, game) => ({
    totalMatches: accumulator.totalMatches + Number(game.matches),
    totalTries: accumulator.totalTries + Number(game.tries),
  }),
  { totalMatches: 0, totalTries: 0 }
);

console.log(reduced);

answered Oct 12, 2018 at 10:22

Lafi

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Comments

arizafar · Accepted Answer · 2018-10-12 10:23:38Z

0

input = [
  {"id": 1,"matches": "123","tries": "11"},
  {"id": 2,"matches": "1","tries": "1"},
  {"id": 3,"matches": "2","tries": "5"}
]

let totalMatches = 0;
let totalTries = 0;
let output = input.reduce(({totalMatches, totalTries}, {matches, tries}) => {
  totalMatches += +matches;
  totalTries += +tries;
  return {totalMatches, totalTries}
},{totalMatches: 0, totalTries: 0});

console.log(output)

answered Oct 12, 2018 at 10:23

arizafar

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