Increment Javascript object member dynamically

Question

Essentially, I desire the function to read all letters from a string, and to spit out an object that contains {'letter', 'count'} properties for each letter.

function freqLetters(string) {
  var freq = [];
  for (var i = 0; i < string.length; i++) {
    var character = string.charAt(i);
    if (typeof freq[character] != undefined) {
      freq[character].count++;
    } else {
      freq.push({'letter': character, 'count': 1});
    }
  }

  return freq;
}

However, freq usually appears empty and when it works, it seems to always fail the '!=== undefined' check and push duplicate letters of 1 count, rather than finding them and increment them.

Is the typeof freq[character] !=== undefined] check correct?

How on earth do I increment dynamic elements?

(i.e. find letter:a if it exists, and increment its count by 1 if it exists)

Try setting the if as if(typeof freq[character] != "undefined").... — FDavidov
– FDavidov, Commented Jul 28, 2016 at 5:53
It says there is an undefined member of 'count' now.. I try freq[character].count++; and all sorts of while testing, and it seems to just append to the array as if it's a new letter each time(so likely the != undefined still fails) (oops I fixed the ] typo) — Sasha
– Sasha, Commented Jul 28, 2016 at 6:00
Ah!! I'm now noticing that you are using the character as index... I wouldn't do that.... — FDavidov
– FDavidov, Commented Jul 28, 2016 at 6:05
As for the if, the != "undefined" part is correct. The problem is with the left part. — FDavidov
– FDavidov, Commented Jul 28, 2016 at 6:06

Piercey4 · Accepted Answer · 2016-07-28 06:07:53Z

2

Functional programming woo.

var counts = string
    .split('') // Get individual letters.
    .reduce((acc, letter)=> {
        // acc is an object (passed in as second arg to reduce).
        // we use the existing value for the letter (default to 0) and add one each time.
        acc[letter] = (acc[letter] || 0) + 1
        return acc
    }, {})

Edit: Realized you wanted an array or { letter: count } objects.

var countsList = Object
    .keys(counts)
    .map((key)=> ({ [key]: counts[key] }))

edited Jul 28, 2016 at 6:07

answered Jul 28, 2016 at 5:59

Piercey4

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4 Comments

Xeren Narcy Over a year ago

can make it smaller still changing (key)=> { return { [key]: counts[key] } } to (key)=>({ [key]: counts[key] })

Piercey4 Over a year ago

Dude. I never thought about wrapping the returned objects in parans to avoid using returns. Your the bomb.

Xeren Narcy Over a year ago

Nor did I, heh, but it came up recently so thought I'd share

Piercey4 Over a year ago

I've used it for 'object switches' like x = ({ a: 1, b: 2, c: 3 })['c'] which is cool but not this.

Silvinus · Accepted Answer · 2016-07-28 05:58:56Z

0

If you want to check existence of letter, don't use an array object. Because push function add element indexed by number (0, 1, 2) so freq[character] is always undefined.

For your instanciation :

var freq = {};

in your else :

freq[character] = {'letter': character, 'count': 1}

And in your if, check just the existence :

if (freq[character]) {... }

answered Jul 28, 2016 at 5:58

Silvinus

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1 Comment

Xeren Narcy Over a year ago

Also if you're super paranoid about the presence of keys, you can use if (character in freq) { ... }

Karthikeyan · Accepted Answer · 2016-07-28 06:24:46Z

0

You could use the below code:

function countCharacters(exampleString){
var countObject = {} ; 
for (var i = 0, l = exampleString.length; i < l; i++) {
    var currentChar =  exampleString.charAt(i);
    if(typeof(currentChar) != undefined) {
        countObject[currentChar] = characterCount(exampleString, currentChar);
    }
}
console.log(countObject);
return(countObject); }



function characterCount(word, character) {
   var count = 0;
    for (var i = 0; i < word.length; i++) {
       if (word[i] === character) {
           count++;
       }
  }
  return count; }

Hope it helps :)

answered Jul 28, 2016 at 6:24

Karthikeyan

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