CODEWITHSUNDEEP
elasticsearchkibanavega-litevega
Ganymede
Ganymede

Reputation: 23

Vega Lite / Kibana - Area Mark shows no values

I have a pretty straightforward problem but I'm totally new to Vega/Vega-Lite and the tutorials examples don't help me much to resolve my issue.

When I try to display my floating point values only Mark: Point/Bar seems to work. Everything else that demands a connection between neighboring points seems to fail, like "Area" or "Line".

What have I missed in order to connect my values to a Area-Chart? Aggregation? Layer? Is the timestamp values calculation wrong?

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "data": {
    "url": {
      "%context%": true,
      "%timefield%": "@timestamp",
      "index": "default-*",
      "body": {"size": 10000, "_source": ["@timestamp", "numericData"]}
    },
    "format": {"property": "hits.hits"}
  },
  "transform": [
    {"calculate": "toDate(datum._source['@timestamp'])", "as": "time"}
  ],
  "vconcat": [
    {
      "width": 1200,
      "mark": {"type": "area", "line": true, "point": true},
      "encoding": {
        "x": {
          "field": "time",
          "scale": {"domain": {"selection": "brush"}},
          "type": "temporal",
          "axis": {"title": ""}
        },
        "y": {
          "field": "_source.numericData",
          "type": "quantitative",
          "scale": {"domain": [0, 10]}
        }
      }
    },
    {
      "width": 1200,
      "height": 60,
      "mark": {"type": "area", "line": true, "point": true},  // <-- only points are rendered :(
      "selection": {"brush": {"type": "interval", "encodings": ["x"]}},
      "encoding": {
        "x": {"field": "time", "type": "temporal"},
        "y": {
          "field": "_source.numericData",
          "type": "quantitative",
          "formatType": "String",
          "axis": {"tickCount": 3, "grid": false}
        }
      }
    }
  ]
}

Points are visible - the values are there but the Area doesn't get rendered because, I suspect, I need to tell Vega Lite to interpret the numerical float values on Y to be interpreted over the whole timefield.

Screenshot

Upvotes: 2

Views: 533

Answers (1)

jakevdp
jakevdp

Reputation: 86463

You didn't share your data, so I can only guess why this is happening. But one reason you might see this result is if there are null values interspersed in your data. Here is a simple example of this (open in editor):

{
  "data": {
    "values": [
      {"x": 1, "y": 1},
      {"x": 2, "y": null},
      {"x": 3, "y": 2},
      {"x": 4, "y": null},
      {"x": 5, "y": 3},
      {"x": 6, "y": null}
    ]
  },
  "mark": {"type": "area", "point": true, "line": true},
  "encoding": {
    "x": {"field": "x", "type": "quantitative"},
    "y": {"field": "y", "type": "quantitative"}
  }
}

enter image description here

Unlike ponts, lines and areas are defined not via single values, but via adjacent values. Because there are no pairs of adjacent non-null values, there is no place where a line or area will be drawn.

If this is the case, you can remove the null points with an appropriate filter transform (open in editor):

{
  "data": {
    "values": [
      {"x": 1, "y": 1},
      {"x": 2, "y": null},
      {"x": 3, "y": 2},
      {"x": 4, "y": null},
      {"x": 5, "y": 3},
      {"x": 6, "y": null}
    ]
  },
  "transform": [{"filter": "isValid(datum.y)"}],
  "mark": {"type": "area", "point": true, "line": true},
  "encoding": {
    "x": {"field": "x", "type": "quantitative"},
    "y": {"field": "y", "type": "quantitative"}
  }
}

enter image description here

Upvotes: 1

Related Questions