Generate map from string array

Question

I'm trying to store some server names in a map based on some predefined logic.

For example if the names are:

"temp-a-name1", "temp-a-name2", "temp-b-name1", "temp-b-name2"

They'll be stored in a map as:

{
  a: [
    "temp-a-name1",
    "temp-a-name2"
  ],
  b: [
    "temp-b-name1",
    "temp-b-name2"
  ]
}

The first letter between the two "-" will always be the key

I'm not too familiar with javascript so I've done this the naive way but I was wondering if there's a better, more javascripty way to do this.

const servers = ["temp-a-name1", "temp-a-name2", "temp-b-name1", "temp-b-name2"];

let map = {};
let key;
for (const server of servers) {
  key = server.charAt(server.indexOf("-") + 1);
  if (key in map) {
    map[key].push(server);
  } else {
    map[key] = [server];
  }
}

Stick with your version. IMO code is readable and easy to understand, so there is no need for refactoring. BTW, such questions are better suitable for codereview.stackexchange.com. — zett42
– zett42, Commented Sep 13, 2019 at 21:55

JamieT · Accepted Answer · 2019-09-13 22:30:16Z

3

You could use the reduce() function:

let servers = ["temp-a-name1", "temp-a-name2", "temp-b-name1", "temp-b-name2"];

let map = servers.reduce((acc, server) => {
  let key = server.charAt(server.indexOf("-") + 1);

  if (acc[key])
    acc[key].push(server);
  else
    acc[key] = [server];
    
  return acc;
}, {})

console.log(map)

edited Sep 13, 2019 at 22:30

answered Sep 13, 2019 at 21:51

JamieT

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1 Comment

charlietfl Over a year ago

reduce() is not an ES6 feature

Danny Buonocore · Accepted Answer · 2019-09-13 21:51:21Z

1

Try this:

const servers = ["temp-a-name1", "temp-a-name2", "temp-b-name1", "temp-b-name2"];
const result = servers.reduce((acc, cur) => ({
    ...acc,
  [cur.split('-')[1]]: (acc[cur.split('-')[1]] || []).concat([cur]),
}), {})
console.log(result);

I think this counts as "javascripty"

answered Sep 13, 2019 at 21:51

Danny Buonocore

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Comments

Toby Mellor · Accepted Answer · 2019-09-13 22:02:08Z

1

I would use reduce. A naive way of getting the key could be .split('-')[1].

const names = ['temp-a-name1', 'temp-a-name2', 'temp-b-name1', 'temp-b-name2'];
const map = names.reduce((map, name) => {
  const key = name.split('-')[1];
  const namesWithKey = map[key] || [];

  return { ...map, [key]: [...namesWithKey, name] };
}, {});

console.log(map);

answered Sep 13, 2019 at 22:02

Toby Mellor

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V. Sambor · Accepted Answer · 2019-09-13 22:05:28Z

1

You can also use the new Map data structure something like this:

const servers = ["temp-a-name1", "temp-a-name2", "temp-b-name1", "temp-b-name2"];

const map = new Map();

servers.forEach(item => {
  const key = item.split('-')[1];
  const value = map.get(key) || [];
  value.push(item);
  
  map.set(key, value);
});

// CONSOLE LOG
for (var [key, value] of map.entries()) {
  console.log(key + ' = ' + value);
}

answered Sep 13, 2019 at 22:05

V. Sambor

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