In Vega-lite, how do I filter by time? - vega-lite

Question

I have a CSV with a row per 15-minute interval and columns for metrics like airflow and temperature. I'd like to filter the data so I can plot only the most recent day or week.
How do I add a filter for a date (Mar 9) or date range (Mar 6–12)? Is it more common to do filtering and aggregation (to hourly or daily averages) before handing the data to Vega-Lite?
Here's my code without a filter:
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"title": "Average Airflow",
"description": "Average Airflow in Rooms",
"data": {"url": "hvac_data-wide.csv"},
"mark": "line",
"width": 608,
"height": 342,
"transform": [{
"timeUnit":"dayhours",
"field": "Date",
"as": "hours"
}],
"encoding": {
"x": {"field": "hours", "type": "temporal", "title": "Time"},
"y": {"field": "SaFl", "type": "quantitative", "aggregate": "mean", "title": "Source Air CFM"},
"color": {"field": "Floor", "type": "nominal"}
}
}
Here's some sample data:
Date,Category,Floor,Name,HVACModeStatus,RmTmp,SaFl,EaFl,CO2,NPW,ChW,wh,kwh
2022-03-07 08:10,zone,1,Lab1115,4,70.88,374.717,1109.641,,,,,
2022-03-07 08:10,zone,1,Lab1121,4,70.16,1700.559,1897.229,,,,,
2022-03-07 08:10,zone,1,Lab1126,2,73.22,1061.672,1572.01,,,,,
2022-03-07 08:15,zone,1,Lab1115,4,70.88,349.848,1170.564,,,,,
2022-03-07 08:15,zone,1,Lab1121,4,70.16,1699.6,1870.382,,,,,
2022-03-07 08:15,zone,1,Lab1126,2,73.22,1092.875,1606.451,,,,,
2022-03-07 08:20,zone,1,Lab1115,4,70.88,376.867,1156.398,,,,,
2022-03-07 08:20,zone,1,Lab1121,4,70.16,1692.929,1875.636,,,,,
2022-03-07 08:20,zone,1,Lab1126,2,73.22,1148.222,1580.696,,,,,
Thank you in advance.

Answer 1

Short answer: Filters can be added within the transform.
Here's code to show a date range filter:
{
"$schema": "https://vega.github.io/schema/vega-lite/v5.json",
"title": "Average Airflow",
"description": "Average Airflow in Rooms",
"data": {"url": "hvac_data-wide.csv"},
"mark": "line",
"width": 608,
"height": 342,
"transform": [
{
"timeUnit":"dayhours",
"field": "Date",
"as": "hours"
},
{"filter": {"field": "Date",
"range": [ {"year": 2022, "month": 3, "date": 8, "hours": 0},
{"year": 2022, "month": 3, "date": 8, "hours": 24, "minutes": 59}]}}
],
"encoding": {
"x": {"field": "hours", "type": "temporal", "title": "Time"},
"y": {"field": "SaFl", "type": "quantitative", "aggregate": "mean", "title": "Exhaust CFM"},
"color": {"field": "Floor", "type": "nominal"}
}
}
They can also be simple expression string, substitute this filter block: { "filter": "datum.Floor == 3"}
Or a primitive: { "filter": {"field": "Floor", "equal": 3}}
More info about filters on the Vega-Lite docs Predicate page.