modify example

Author: kanitw

examples/specs/bar_grouped_timeunit_yearweek.vl.json

@@ -2,6 +2,7 @@
   "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
   "width": 400,
   "height": 250,
+  "transform": [{"filter": {"timeUnit": "year", "field": "Year", "range": [1970, 1971]}}],
   "data": {"url": "data/cars.json"},
   "mark": "bar",
   "encoding": {