Trying to add values of same key but with iterating it. here is my array

```
arr = [ {a: 10, b: 5, c: 2}, {a: 5, c: 3}, { b: 15, c: 4}, {a: 2}, {} ]

```

Want to converted it like

```
{a: 17, b: 20, c: 9} 

```