Question

How to group words in a string by the first N letters in JavaScript

Answer 1

function groupByFirstNLetters(s, n = 3) {
  const words = s.toLowerCase().match(/[a-zA-Z]+/g) || [];
  const groups = {};

  for (const w of words) {
    if (w.length >= n) {
      const prefix = w.slice(0, n);
      if (!groups[prefix]) groups[prefix] = [];
      groups[prefix].push(w);
    }
  }

  return groups;
}

const s = "The lowly inhabitants of the lowland were surprised to see the lower branches of the trees.";

const groups = groupByFirstNLetters(s, 3);

// Print version 1
for (const [prefix, words] of Object.entries(groups)) {
  console.log(prefix, ":", words);
}

console.log();

// Print version 2
for (const [prefix, words] of Object.entries(groups)) {
  console.log(`${prefix}: ${words.join(", ")}`);
}



/*
run:

the : [ 'the', 'the', 'the', 'the' ]
low : [ 'lowly', 'lowland', 'lower' ]
inh : [ 'inhabitants' ]
wer : [ 'were' ]
sur : [ 'surprised' ]
see : [ 'see' ]
bra : [ 'branches' ]
tre : [ 'trees' ]

the: the, the, the, the
low: lowly, lowland, lower
inh: inhabitants
wer: were
sur: surprised
see: see
bra: branches
tre: trees

*/

 

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Answer 2

function groupByFirstNLetters(s, n = 3) {
  return (s.toLowerCase().match(/[a-zA-Z]+/g) || [])
    .filter(w => w.length >= n)
    .reduce((groups, w) => {
      const prefix = w.slice(0, n);
      (groups[prefix] ||= []).push(w);
      return groups;
    }, {});
}

const s = "The lowly inhabitants of the lowland were surprised to see the lower branches of the trees.";

const groups = groupByFirstNLetters(s, 3);

// Print version 1
for (const [prefix, words] of Object.entries(groups)) {
  console.log(prefix, ":", words);
}

console.log();

// Print version 2
for (const [prefix, words] of Object.entries(groups)) {
  console.log(`${prefix}: ${words.join(", ")}`);
}



/*
run:

the : [ 'the', 'the', 'the', 'the' ]
low : [ 'lowly', 'lowland', 'lower' ]
inh : [ 'inhabitants' ]
wer : [ 'were' ]
sur : [ 'surprised' ]
see : [ 'see' ]
bra : [ 'branches' ]
tre : [ 'trees' ]

the: the, the, the, the
low: lowly, lowland, lower
inh: inhabitants
wer: were
sur: surprised
see: see
bra: branches
tre: trees

*/

 

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