My JSON looks like this:

```
json = [
  {
    type: "big"
    date: "2012-12-08"
    qty: 6
  }
  {
    type: "small"
    date: "2012-12-08"
    qty: 9
  }
  {
    type: "big"
    date: "2012-12-15"
    qty: 4
  }
  {
    type: "small"
    date: "2012-12-07"
    qty: 7
  }
  {
    type: "small"
    date: "2012-11-07"
    qty: 3
  }
]    

```

What I'm trying to do is group/merge each `type` that has a `date` with the same year & month (the first 7 characters in the `date` string) and get the sum of those `qty`'s. The output should look like this:

```
json = [
  {
    type: "big"
    date: "2012-12"
    qty: 10
  }
  {
    type: "small"
    date: "2012-12"
    qty: 16
  }
  {
    type: "small"
    date: "2012-11"
    qty: 3
  }
]  

```

There are several similar questions I've found here but haven't come across one that does exactly what I'm looking for. I have played around with lots of code borrowed from different examples but can't quite seem to get the results I need. I'm not home now, therefore I can't paste any code I've tried at the moment but I'm asking for help in hopes to have an answer/solution to test out later