JavaScript Group By Array
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
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;
}, {} );