Hi,

I am trying get the average price of quantities of items sold for a given price.

Here is the data:

```
"data": {
"values": [
{"week": "1", "turnover": 200, "quantity": 100},
{"week": "1", "turnover": 250, "quantity": 110},
{"week": "1", "turnover": 200, "quantity": 100},
{"week": "2", "turnover": 220, "quantity": 100},
{"week": "2", "turnover": 270, "quantity": 120},
{"week": "2", "turnover": 220, "quantity": 100},
{"week": "3", "turnover": 300, "quantity": 150},
{"week": "3", "turnover": 400, "quantity": 170},
{"week": "3", "turnover": 500, "quantity": 190}
]
},
```

For each of the week of [1, 2, 3], I am trying to get the total turnover during that week, divided by the total quantity during that week.

During week 1, the total turnover is 650 items. The total quantity sold is 310 during that same week. So the average price would be 310 / 650 = 0,47.

How can I visualise this average price per week?

The weeks are on the X-axis, and the average price is on the Y-axis.

So far I have tried a few things, the best of which should have been this:

```
{
$schema: https://vega.github.io/schema/vega-lite/v2.json
title: Vega-Lite
"data": {
"values": [
{"week": "1", "turnover": 200, "quantity": 100},
{"week": "1", "turnover": 250, "quantity": 110},
{"week": "1", "turnover": 200, "quantity": 100},
{"week": "2", "turnover": 220, "quantity": 100},
{"week": "2", "turnover": 270, "quantity": 120},
{"week": "2", "turnover": 220, "quantity": 100},
{"week": "3", "turnover": 300, "quantity": 150},
{"week": "3", "turnover": 400, "quantity": 170},
{"week": "3", "turnover": 500, "quantity": 190}
]
},
"transform": [
{
"aggregate": [{
"op": "sum",
"field": "turnover",
"as": "newfield"
}]
}
],
"mark": "point",
"encoding": {
"x": {"field": "week", "type": "ordinal"}
"y": {"field": "price", "type": "quantitative"},
}
}
```

That runs on a Vega-Lite visualization on Kibana.

The above is not the exact correct solution, but this JSON leads to a completely blank visualization, as if the Vega-lite code crashes.

My question is this: How should I calculate this average weekly price and visualise it?

Thank you!

Teus Benschop