Deneb: Combine vconcat and hconcat

Hey Salle, it's tough to determine a proper solution without example data. Nevertheless, below is a spec that includes horizontal and vertical concatenation that is hopefully close to what you're after. If this is enough to get you going, please consider liking and kudoing this message.

If you need more assistance, could provide what you've tried in your spec and a sanitized dataset? (here's how)

I'd be happy to try and help more. 

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A simple bar chart with embedded data.",
  "data": {
    "values": [
      {"a": "A", "b": 28},
      {"a": "B", "b": 55},
      {"a": "C", "b": 43},
      {"a": "D", "b": 91},
      {"a": "E", "b": 81},
      {"a": "F", "b": 53},
      {"a": "G", "b": 19},
      {"a": "H", "b": 87},
      {"a": "I", "b": 52},
      {"a": "J", "b": 19},
      {"a": "K", "b": 87},
      {"a": "L", "b": 52}
    ]
  },
  "title": "Frequency By Letter",
  "hconcat": [
    {
      "vconcat": [
        {
          "transform": [{"filter": {"field": "a", "oneOf": ["A", "B", "C"]}}],
          "mark": "bar",
          "encoding": {
            "x": {"field": "a", "type": "nominal", "axis": {"labelAngle": 0, "title": null}},
            "y": {"field": "b", "type": "quantitative"}
          }
        },
        {
          "transform": [{"filter": {"field": "a", "oneOf": ["G", "H", "I"]}}],
          "mark": "bar",
          "encoding": {
            "x": {"field": "a", "type": "nominal", "axis": {"labelAngle": 0, "title": null}},
            "y": {"field": "b", "type": "quantitative"}
          }
        }
      ]
    },
    {
      "vconcat": [
        {
          "transform": [{"filter": {"field": "a", "oneOf": ["D", "E", "F"]}}],
          "mark": "bar",
          "encoding": {
            "x": {"field": "a", "type": "nominal", "axis": {"labelAngle": 0, "title": null}},
            "y": {"field": "b", "type": "quantitative"}
          }
        },
         {
          "transform": [{"filter": {"field": "a", "oneOf": ["J", "K", "L"]}}],
          "mark": "bar",
          "encoding": {
            "x": {"field": "a", "type": "nominal", "axis": {"labelAngle": 0, "title": null}},
            "y": {"field": "b", "type": "quantitative"}
          }
        }
      ]
    }
  ]
}