{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "The Trellis display by Becker et al. helped establish small multiples as a “powerful mechanism for understanding interactions in studies of how a response depends on explanatory variables”. Here we reproduce a trellis of Barley yields from the 1930s, complete with main-effects ordering to facilitate comparison.",
  "background": "white",
  "padding": 5,
  "data": [
    {"name": "source_0", "url": "data/barley.json", "format": {"type": "json"}},
    {
      "name": "trellis_barley_row_domain",
      "source": "source_0",
      "transform": [
        {
          "type": "aggregate",
          "groupby": ["site"],
          "fields": ["yield"],
          "ops": ["median"],
          "as": ["median_yield"]
        }
      ]
    },
    {
      "name": "data_2",
      "source": "source_0",
      "transform": [
        {
          "type": "aggregate",
          "groupby": ["variety", "year", "site"],
          "ops": ["median"],
          "fields": ["yield"],
          "as": ["median_yield"]
        },
        {
          "type": "filter",
          "expr": "isValid(datum[\"median_yield\"]) && isFinite(+datum[\"median_yield\"])"
        }
      ]
    },
    {
      "name": "data_3",
      "source": "source_0",
      "transform": [
        {
          "type": "aggregate",
          "groupby": ["site"],
          "ops": ["median"],
          "fields": ["yield"],
          "as": ["median_yield"]
        },
        {
          "type": "filter",
          "expr": "isValid(datum[\"median_yield\"]) && isFinite(+datum[\"median_yield\"])"
        }
      ]
    }
  ],
  "signals": [
    {"name": "trellis_barley_child_width", "value": 200},
    {"name": "trellis_barley_y_step", "value": 12},
    {
      "name": "trellis_barley_child_height",
      "update": "bandspace(domain('trellis_barley_y').length, 1, 0.5) * trellis_barley_y_step"
    }
  ],
  "layout": {
    "padding": 20,
    "offset": {"rowTitle": 10},
    "columns": 1,
    "bounds": "full",
    "align": "all"
  },
  "marks": [
    {
      "name": "row-title",
      "type": "group",
      "role": "row-title",
      "title": {
        "text": "site",
        "orient": "left",
        "style": "guide-title",
        "offset": 10
      }
    },
    {
      "name": "trellis_barley_row_header",
      "type": "group",
      "role": "row-header",
      "from": {"data": "trellis_barley_row_domain"},
      "sort": {"field": "datum[\"median_yield\"]", "order": "ascending"},
      "title": {
        "text": {
          "signal": "isValid(parent[\"site\"]) ? parent[\"site\"] : \"\"+parent[\"site\"]"
        },
        "orient": "left",
        "style": "guide-label",
        "frame": "group",
        "offset": 10
      },
      "encode": {
        "update": {"height": {"signal": "trellis_barley_child_height"}}
      },
      "axes": [
        {
          "scale": "trellis_barley_y",
          "orient": "left",
          "grid": false,
          "title": "variety",
          "zindex": 0
        }
      ]
    },
    {
      "name": "trellis_barley_column_footer",
      "type": "group",
      "role": "column-footer",
      "encode": {"update": {"width": {"signal": "trellis_barley_child_width"}}},
      "axes": [
        {
          "scale": "trellis_barley_x",
          "orient": "bottom",
          "grid": false,
          "title": "Median of yield",
          "labelFlush": true,
          "labelOverlap": true,
          "tickCount": {"signal": "ceil(trellis_barley_child_width/40)"},
          "zindex": 0
        }
      ]
    },
    {
      "name": "trellis_barley_cell",
      "type": "group",
      "style": "cell",
      "from": {
        "facet": {
          "name": "trellis_barley_facet",
          "data": "source_0",
          "groupby": ["site"],
          "aggregate": {
            "fields": ["yield"],
            "ops": ["median"],
            "as": ["median_yield_by_site"]
          }
        }
      },
      "sort": {
        "field": ["datum[\"median_yield_by_site\"]"],
        "order": ["ascending"]
      },
      "data": [
        {
          "name": "data_1",
          "source": "trellis_barley_facet",
          "transform": [
            {
              "type": "aggregate",
              "groupby": ["variety", "year"],
              "ops": ["median"],
              "fields": ["yield"],
              "as": ["median_yield"]
            },
            {
              "type": "filter",
              "expr": "isValid(datum[\"median_yield\"]) && isFinite(+datum[\"median_yield\"])"
            }
          ]
        },
        {
          "name": "data_2",
          "source": "trellis_barley_facet",
          "transform": [
            {
              "type": "aggregate",
              "groupby": [],
              "ops": ["median"],
              "fields": ["yield"],
              "as": ["median_yield"]
            },
            {
              "type": "filter",
              "expr": "isValid(datum[\"median_yield\"]) && isFinite(+datum[\"median_yield\"])"
            }
          ]
        }
      ],
      "encode": {
        "update": {
          "width": {"signal": "trellis_barley_child_width"},
          "height": {"signal": "trellis_barley_child_height"}
        }
      },
      "marks": [
        {
          "name": "trellis_barley_child_layer_0_marks",
          "type": "symbol",
          "style": ["point"],
          "from": {"data": "data_1"},
          "encode": {
            "update": {
              "fill": {"value": "transparent"},
              "stroke": {"scale": "trellis_barley_color", "field": "year"},
              "ariaRoleDescription": {"value": "point"},
              "description": {
                "signal": "\"Median of yield: \" + (format(datum[\"median_yield\"], \"\")) + \"; variety: \" + (isValid(datum[\"variety\"]) ? datum[\"variety\"] : \"\"+datum[\"variety\"]) + \"; year: \" + (isValid(datum[\"year\"]) ? datum[\"year\"] : \"\"+datum[\"year\"])"
              },
              "x": {"scale": "trellis_barley_x", "field": "median_yield"},
              "y": {"scale": "trellis_barley_y", "field": "variety"}
            }
          }
        },
        {
          "name": "trellis_barley_child_layer_1_marks",
          "type": "rule",
          "style": ["rule"],
          "from": {"data": "data_2"},
          "encode": {
            "update": {
              "stroke": {"value": "black"},
              "description": {
                "signal": "\"Median of yield: \" + (format(datum[\"median_yield\"], \"\"))"
              },
              "x": {"scale": "trellis_barley_x", "field": "median_yield"},
              "y": {"value": 0},
              "y2": {"field": {"group": "height"}}
            }
          }
        }
      ],
      "axes": [
        {
          "scale": "trellis_barley_x",
          "orient": "bottom",
          "gridScale": "trellis_barley_y",
          "grid": true,
          "tickCount": {"signal": "ceil(trellis_barley_child_width/40)"},
          "domain": false,
          "labels": false,
          "aria": false,
          "maxExtent": 0,
          "minExtent": 0,
          "ticks": false,
          "zindex": 0
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "trellis_barley_x",
      "type": "linear",
      "domain": {
        "fields": [
          {"data": "data_2", "field": "median_yield"},
          {"data": "data_3", "field": "median_yield"}
        ]
      },
      "range": [0, {"signal": "trellis_barley_child_width"}],
      "zero": false,
      "nice": true
    },
    {
      "name": "trellis_barley_y",
      "type": "point",
      "domain": {
        "data": "source_0",
        "field": "variety",
        "sort": {"op": "median", "field": "yield", "order": "descending"}
      },
      "range": {"step": {"signal": "trellis_barley_y_step"}},
      "padding": 0.5
    },
    {
      "name": "trellis_barley_color",
      "type": "ordinal",
      "domain": {"data": "data_2", "field": "year", "sort": true},
      "range": "category"
    }
  ],
  "legends": [
    {
      "stroke": "trellis_barley_color",
      "symbolType": "circle",
      "title": "year",
      "encode": {"symbols": {"update": {"fill": {"value": "transparent"}}}}
    }
  ]
}