Vega-Lite — retention cohort heatmap

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"values": [
    {"cohort":"Jan","week":0,"r":100},{"cohort":"Jan","week":1,"r":68},{"cohort":"Jan","week":2,"r":55},
    {"cohort":"Feb","week":0,"r":100},{"cohort":"Feb","week":1,"r":72},{"cohort":"Feb","week":2,"r":58},
    {"cohort":"Mar","week":0,"r":100},{"cohort":"Mar","week":1,"r":74},{"cohort":"Mar","week":2,"r":63}
  ]},
  "mark":"rect",
  "encoding": {
    "x":{"field":"week","type":"ordinal"},
    "y":{"field":"cohort","type":"nominal"},
    "color":{"field":"r","type":"quantitative","scale":{"scheme":"blues"}}
  }
}