count of word occurrences in a list, case insensitive

Question

What is the most professional way to obtain a case insensitive count of the distinct words contained in an array using plain javascript? I have done the first attempt myself but does not feel much professional.

I would like the result to be a Map

Answer 1

You can use Array.reduce to store each word as a property and the occurrence of each as the value.

In the reducer function, check whether the letter (converted to lowercase) exists as a property. If not, set its value to 1. Otherwise, increment the property value.

const arr = ["a", "A", "b", "B"]

const result = arr.reduce((a,b) => {
  let c = b.toLowerCase();
  return a[c] = a[c] ? ++a[c] : 1, a;
}, {})

console.log(result)

_{As a one liner: const result = arr.reduce((a,b) => (c = b.toLowerCase(), a[c] = a[c] ? ++a[c] : 1, a), {})}

To convert it to a Map, you can use Object.entries (sugged by @Théophile):

const arr = ["a", "A", "b", "B"]

const result = arr.reduce((a, b) => {
  let c = b.toLowerCase();
  return a[c] = a[c] ? ++a[c] : 1, a;
}, {})

const m = new Map(Object.entries(result))
m.forEach((value, key) => console.log(key, ':', value))