Dynamic Top N: window rank + filter

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      { "message": "timeout DB" }, { "message": "timeout DB" }, { "message": "timeout DB" },
      { "message": "timeout DB" }, { "message": "timeout DB" }, { "message": "timeout DB" },
      { "message": "connexion refusée" }, { "message": "connexion refusée" }, { "message": "connexion refusée" },
      { "message": "connexion refusée" }, { "message": "connexion refusée" },
      { "message": "OOM worker" }, { "message": "OOM worker" }, { "message": "OOM worker" }, { "message": "OOM worker" },
      { "message": "certificat expiré" }, { "message": "certificat expiré" }, { "message": "certificat expiré" },
      { "message": "quota dépassé" }, { "message": "quota dépassé" },
      { "message": "schéma invalide" }, { "message": "schéma invalide" },
      { "message": "disque plein" },
      { "message": "DNS introuvable" },
      { "message": "rate limit atteint" },
      { "message": "deadlock SQL" }
    ]
  },
  "transform": [
    { "aggregate": [{ "op": "count", "as": "n" }], "groupby": ["message"] },
    {
      "window": [{ "op": "rank", "as": "rang" }],
      "sort": [{ "field": "n", "order": "descending" }]
    },
    { "filter": "datum.rang <= 8" }
  ],
  "mark": "bar",
  "encoding": {
    "y": { "field": "message", "type": "nominal", "sort": "-x", "title": null },
    "x": { "field": "n", "type": "quantitative", "title": "Occurrences" }
  }
}