javascript - Group array of strings by first letter - Stack Overflow

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I have this challenge, which consists on:

• Writing a function that takes an array of strings as argument
• Then, group the strings in the array by their first letter
• Return an object that contains properties with keys representing first letters

For example:

Should return

groupIt(['hola', 'adios', 'chao', 'hemos', 'accion'])

// Should return
{ 
 a: [ "adios", "accion" ]
 c: [ "chao" ]
 h: [ "hola", "hemos" ]
​}

This is my answer, it returns the expected object, but doesn't pass the test in the page:

function groupIt(arr) {
  let groups = {}
  
  let firstChar = arr.map(el=>el[0])
  let firstCharFilter = firstChar.filter((el,id)=>{
    return firstChar.indexOf(el)===id
  })
 
  firstCharFilter.forEach(el=>{
    groups[el]=[]
  })
  
  firstCharFilter.forEach(char=>{
    for(let word of arr) {
      if(word[0]==char) {
        groups[char].push(word)
      }
    }
  })
    
  return groups
}

const result = groupIt(['hola', 'adios', 'chao', 'hemos', 'accion']);

console.log(result);

I have this challenge, which consists on:

• Writing a function that takes an array of strings as argument
• Then, group the strings in the array by their first letter
• Return an object that contains properties with keys representing first letters

For example:

Should return

groupIt(['hola', 'adios', 'chao', 'hemos', 'accion'])

// Should return
{ 
 a: [ "adios", "accion" ]
 c: [ "chao" ]
 h: [ "hola", "hemos" ]
​}

This is my answer, it returns the expected object, but doesn't pass the test in the page:

function groupIt(arr) {
  let groups = {}
  
  let firstChar = arr.map(el=>el[0])
  let firstCharFilter = firstChar.filter((el,id)=>{
    return firstChar.indexOf(el)===id
  })
 
  firstCharFilter.forEach(el=>{
    groups[el]=[]
  })
  
  firstCharFilter.forEach(char=>{
    for(let word of arr) {
      if(word[0]==char) {
        groups[char].push(word)
      }
    }
  })
    
  return groups
}

const result = groupIt(['hola', 'adios', 'chao', 'hemos', 'accion']);

console.log(result);

Where am I failing at?

Here the test: https://www.jschallenger./javascript-arrays/javascript-group-array-strings-first-letter

• javascript
• arrays

Share Improve this question Follow edited Nov 19, 2022 at 22:59 Andy 63.6k1313 gold badges7171 silver badges9898 bronze badges asked Feb 18, 2022 at 18:35 Juan LuisJuan Luis 13311 silver badge88 bronze badges 2

• Don't bother to set the keys up first. You'll have to redo that work when figuring out where to insert the words. Instead, for each word: get the key; if that key does not already exist, add the key; add the word. – Ouroborus Commented Feb 18, 2022 at 19:05
• Also, the puzzle author's solution isn't that great. It seems designed to look cool to people with less knowledge but has obvious performance issues. – Ouroborus Commented Feb 18, 2022 at 19:14

Add a ment  | 

8 Answers 8

Sorted by: Reset to default 3

I ran your code as well as the test examples provided by JS challenger. I noticed that they where case sensitive. So although your code works well, if the words begin with upper case it will not pass certain cases. Attached is my version that passed all test examples.

If you add : .toLowerCase to the firstChar, I believe you will pass as well. Happy coding ;)

P.S if the image below does not work please let me know, I am just learning how to contribute to Stack Exchange, thanks.

const groupIt = (array) => {
  let resultObj = {};
  
  for (let i =0; i < array.length; i++) {
    let currentWord = array[i];
    let firstChar = currentWord[0].toLowerCase();
    let innerArr = [];
    if (resultObj[firstChar] === undefined) {
       innerArr.push(currentWord);
      resultObj[firstChar] = innerArr
    }else {
      resultObj[firstChar].push(currentWord)
    }
  }
  return resultObj
}

console.log(groupIt(['hola', 'adios', 'chao', 'hemos', 'accion']))

console.log(groupIt(['Alf', 'Alice', 'Ben'])) // { a: ['Alf', 'Alice'], b: ['Ben']}

console.log(groupIt(['Ant', 'Bear', 'Bird'])) // { a: ['Ant'], b: ['Bear', 'Bird']}
console.log(groupIt(['Berlin', 'Paris', 'Prague'])) // { b: ['Berlin'], p: ['Paris', 'Prague']}

The site doesn't like .reduce, but here's one way:

const r1 = groupIt(['hola', 'adios', 'chao', 'hemos', 'accion'])
console.log(r1)

// Should return
// {
//   a: ["adios", "accion"]
//   c: ["chao"]
//   h: ["hola", "hemos"]
// }

function groupIt(arr) {
  return arr.reduce((store, word) => {
    const letter = word.charAt(0)
    const keyStore = (
      store[letter] ||     // Does it exist in the object?
      (store[letter] = []) // If not, create it as an empty array
    ); 
    keyStore.push(word)

    return store
  }, {})
}

Case sensitive is the reason. Pop a toLowerCase in after the charAt(0).

Here's my example:

https://stackblitz./edit/node-tebpdp?file=ArrayStringsFirstLetter.js

Link to screenshot!

You could take Object.groupBy with a callback for the grouping constraint.

const
    groupIt = array => Object.groupBy(array, ([c]) => c.toLowerCase());

console.log(groupIt(['hola', 'adios', 'chao', 'hemos', 'accion']));

.as-console-wrapper { max-height: 100% !important; top: 0; }

You code is correct, the only wrong part is that you are not lowercasing the first letter, here is your code with additional lowercasing of the first letter, so it passes the test:

function groupIt(arr) {
  let groups = {}
  
  let firstChar = arr.map(el=>el[0])
  let firstCharFilter = firstChar.filter((el,id)=>{
    return firstChar.indexOf(el)===id
  })
 
  firstCharFilter.forEach(el=>{
    groups[el.toLowerCase()]=[]
  })
  
  firstCharFilter.forEach(char=>{
    for(let word of arr) {
      if(word[0]==char) {
        groups[char.toLowerCase()].push(word)
      }
    }
  })
    
  return groups;
}

const groupIt = (arr) => {
  
  return arr.reduce((acc, cur) => {
    const firstLetter = cur[0].toLowerCase();
    return { ...acc, [firstLetter]: [...(acc[firstLetter] || []), cur] };
  }, {});
};

function groupIt(arr) {
  var obj = {};
  arr.forEach(e => obj[e[0].toLowerCase()] = arr.filter(ele => ele[0].toLowerCase() == e[0].toLowerCase()));
  return obj;
}
console.log(groupIt(['Alf', 'Alice', 'Ben'])); //{ a: [ 'Alf', 'Alice' ], b: [ 'Ben' ] }
console.log(groupIt(['Ant', 'Bear', 'Bird'])); // { a: [ 'Ant' ], b: [ 'Bear', 'Bird' ] }
console.log(groupIt(['Berlin', 'Paris', 'Prague'])); // { b: [ 'Berlin' ], p: [ 'Paris', 'Prague' ] }

Here's my example:

function myFunction(arr){
let count = {}
     arr.forEach((e, i)=>{
         count[e.charAt(0)] = [...count[e.charAt(0)] || [],e]
     })
 return count
}
myFunction(['hola', 'adios', 'chao', 'hemos', 'accion'])

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