How to count string occurrences in an array of strings in TypeScript? [duplicate]

Question

I need to iterate over an array of strings, count the occurrences of each string, and return a object with the value and the number of occurrences.

I'm trying to use the array reduce function to achieve such thing, but, despite the attempts, I haven't been able to achieve that yet.

So I have the following:

["tony", "tony", "tony", "tony", "kassandra", "tony", "tony", "kassandra"]

I need the output:

[{ name: "tony", matches: 6 }, { name: "kassandra", matches: 2 }]

What should I use to obtain the above output?

I have tried the following:

const names = nameList.map((user) => user.name);

const reduce = names.reduce((p, c) => {
  if (p == c) {
    return { name: p, matches: `idk what put here yet` };
  }
  return c;
});

Answer 1

Firstly, count the occurrences of each name in the array.
Secondly, convert it into an object with the desired format of name and their matches.

const names = ["tony", "tony", "tony", "tony", "kassandra", "tony", "tony", "kassandra"];
const counts = {};
//1.
names.forEach(name => {
  if (counts[name]) {
    counts[name] += 1;
  } else {
    counts[name] = 1;
  }
});
//2.
const result = Object.keys(counts).map(name => {
  return {
    name: name,
    matches: counts[name]
  };
});
console.log(result);

If you want to use .reduce() approach to counting occurrences of names:

const counts = names.reduce((acc, name) => {
    acc[name] = (acc[name] || 0) + 1;
    return acc;
  }, {});

Another approach to convert occurrences back into an object using Object.entries()

Object.entries(counts).map(([name, matches]) => ({ name, matches }));

Two approaches combined:

const names = ["tony", "tony", "tony", "tony", "kassandra", "tony", "tony", "kassandra"];
const counts = names.reduce((acc, name) => {
    acc[name] = (acc[name] || 0) + 1;
    return acc;
  }, {});
const result = Object.entries(counts).map(([name, matches]) => ({ name, matches }));
console.log(result);