Vega-lite heatmap "transform" isn't working right - elasticsearch

Question

1) There's a X - coordinate and Y - coordinate. There's a Z - value. Z needs to calculate AVG.
"data": {
"values": [
{"x": 0, "y": 0, "z": 0},
{"x": 1, "y": 0, "z": 1},
{"x": 2, "y": 0, "z": 5},
{"x": 2, "y": 0, "z": 10},
{"x": 4, "y": 0, "z": 16},
{"x": 0, "y": 1, "z": 1},
{"x": 1, "y": 1, "z": 2},
{"x": 2, "y": 1, "z": 5},
{"x": 3, "y": 1, "z": 10},
{"x": 5, "y": 1, "z": 26}
]},
If the data:
"encoding": {
"x": {"field": "x", "type": "ordinal", "title": "X"},
"y": {"field": "y", "type": "ordinal", "title": "Y"} },
then AVG that's right:
Vega Editor
If I use "transform" with "groupby" :
"transform": [ {"window": [{"op": "count", "field": "x", "as": "x2"}], "groupby": ["y"]}],
"encoding": {
"x": {"field": "x2", "type": "ordinal", "title": "X"},
"y": {"field": "y", "type": "ordinal", "title": "Y"}
},
then AVG it's not true:
Vega Editor

Answer 1

The transform is doing exactly what you're telling it to do:
{"window": [{"op": "count", "field": "x", "as": "x2"}], "groupby": ["y"]}
It groups your data by y. Schematically it looks like this:
y=0: x: [0, 1, 2, 2, 4]
z: [0, 1, 5, 10, 16]
y=1: x: [0, 1, 2, 3, 5]
z: [1, 2, 5, 10, 26]
Then it does a sliding window and assigns the count to x2:
y=0: x: [0, 1, 2, 2, 4]
z: [0, 1, 5, 10, 16]
x2: [1, 2, 3, 4, 5]
y=1: x: [0, 1, 2, 3, 5]
z: [1, 2, 5, 10, 26]
x2: [1, 2, 3, 4, 5]
As you can see, when you create a plot of y vs x2, there is now a single z value at each location, and this is correctly reflected in the chart that you show above.
If you want different behavior, you should specify a different transform.