Create and populate array dynamically with javascript

Question

I have an array of programming language like:

const tags = ["js", "ruby", "ios", "python", "go"];

I also have a list of users like:

const user = [
  {
    "id": "userId_1",
    "language": ["ruby", "ios"]
  }, 
  ...
];

Is there a nice way to populate an array named by the language name with the Ids of users?

Something like:

const ruby = ["userId_1", "userId_3", "userId_8", ...];

@WilliamWang I meant that the variable name ruby gets erased. You must store it in a scoped name. — Mr. Polywhirl
– Mr. Polywhirl, Commented Jan 19, 2021 at 14:26
ah, yes, correct. according to my answer, we should call it by output.ruby, ... — topdev87
– topdev87, Commented Jan 19, 2021 at 14:27

topdev87 · Accepted Answer · 2021-01-19 14:20:54Z

4

You can use Array.reduce().

const tags = ["js", "ruby", "ios", "python", "go"];

const user = [
  {
    "id": "userId_1",
    "language": ["ruby", "ios"]
  }, 
  {
    "id": "userId_2",
    "language": ["ruby", "python"]
  }, 
  {
    "id": "userId_3",
    "language": ["go", "ios"]
  }, 
];

const output = user.reduce((acc, cur) => {
  cur.language.forEach(lang => {
    if (!acc[lang]) acc[lang] = [];
    acc[lang].push(cur.id);
  });
  return acc;
}, {});

console.log(output);

answered Jan 19, 2021 at 14:20

topdev87

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5 Comments

Xavier Over a year ago

You don't even need the tags array right?

topdev87 Over a year ago

correct for now, just tags will be needed if you needs all the tags in the output to refactor the output.

Xavier Over a year ago

Hum, I got something like { '[object Object]': [ 'userId_1', 'userId_2',

topdev87 Over a year ago

can you run the above code snippet ? result says

{   "ruby": [     "userId_1",     "userId_2"   ],   "ios": [     "userId_1",     "userId_3"   ],   "python": [     "userId_2"   ],   "go": [     "userId_3"   ] }

Xavier Over a year ago

Yeah, nevermind my "real world code" just had a type issue (basically language is an object! Thanks for your help man!

Hugo Martin · Accepted Answer · 2021-01-19 14:32:38Z

0

Something shorter would be nice:

const ruby = user.map((user) => user.language.includes("ruby") ? user.id : undefined);

answered Jan 19, 2021 at 14:32

Hugo Martin

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