JavaScript Group By Array

Question

Possible Duplicate:
array_count_values for javascript instead

Let's say I have simple JavaScript array like the following:

var array = ['Car', 'Car', 'Truck', 'Boat', 'Truck'];

I want to group and count of each so I would expect a key/value map of:

{
  Car   : 2,
  Truck : 2,
  Boat  : 1
}

Answer 1

var arr = [ 'Car', 'Car', 'Truck', 'Boat', 'Truck' ]; var hist = {}; arr.map( function (a) { if (a in hist) hist[a] ++; else hist[a] = 1; } ); console.log(hist); 

results in

{ Car: 2, Truck: 2, Boat: 1 } 

This works, too:

hist = arr.reduce( function (prev, item) {    if ( item in prev ) prev[item] ++;    else prev[item] = 1;    return prev;  }, {} ); 

Answer 2

You can loop through each index and save it in a dictionary and increment it when every that key is found.

count = {};
for(a in array){
  if(count[array[a]])count[array[a]]++;
  else count[array[a]]=1;
}

Output will be:

Boat: 1
Car: 2
Truck: 2