Adding an element to an object in a for loop

Question

I want to populate an object with the run length encoding of a string. Using an array this would generally be pretty simple, but I'm not quite sure what to do for an object.

function addto (string) {  
   var string = string.split("").sort();
   var cnt = 1;
   var obj = {};

   for (i = 0; i < string.length; i ++) {
     if (string[i] === string[i+1])
       cnt++;

   }

   return obj;
}

addto("abbccc");

Now obviously I can't use a method like push() here. But I also can't set the object name to the string at position i like so:

obj.string[i] = cnt;

Which is what I initially hoped to do. Is there a proper way to do this so that my output would be (for the example given):

{"a":1, "b":2, "c":3}

000 · Accepted Answer · 2014-04-24 01:51:29Z

3

For every character in the string, you want to increment the obj counter for that character once. Here is a push in the right direction.

var obj = {};
for (i = 0; i < string.length; i ++) {
  // If the character has not been seen yet, set its counter to 0.
  obj[string[i]] = obj[string[i]] || 0;
  // Increment that character's count once.
  obj[string[i]]++;
}

Note that with this direction, you do not need to sort the array beforehand.

Here's another alternative. If you're doing this as coursework, then don't use this. But as a mental exercise I leave the solution:

var str = "abbccccddeeeeefgh"
var matches = str.match(/(.)\1*/g);
// matches = ["a", "bb", "cccc", "dd", "eeeee", "f", "g", "h"]
var counts = {};
for (i in matches)
  counts[matches[i][0]] = matches[i].length;
// counts = Object {a: 1, b: 2, c: 4, d: 2, e: 5, f: 1, g: 1, h: 1}

edited Apr 24, 2014 at 1:51

answered Apr 24, 2014 at 1:39

000

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1 Comment

Xelad1 Over a year ago

Thanks Joe, this was just what I was looking for, I'll accept as soon as I can!

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