vega-lite 条形图上的一致梯度

Question

是否可以在 vega 或 vega lite 中创建在整个图表中具有固定梯度的条形图，而不是每个条形都有单独的梯度？

我尝试在标记上使用渐变颜色/填充，但它为每个条形创建了一个新的渐变：

这是我在 Vega 编辑器

中尝试过的代码

Answer 1

考虑到渐变的创建方式，我认为这是相当困难的。这是一种简单的方法，先绘制完整的条形，然后在顶部绘制白色的条形，以达到所需的结果。由于 zindex 问题，网格线不会相同，但这对您来说可能是一个足够好的解决方案。

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "background": "white",
  "padding": 5,
  "height": 200,
  "style": "cell",
  "data": [
    {
      "name": "source_0",
      "values": [
        {"date": "2024-08-25", "views": 30},
        {"date": "2024-08-26", "views": 7},
        {"date": "2024-08-27", "views": 12},
        {"date": "2024-08-28", "views": 15},
        {"date": "2024-08-29", "views": 8},
        {"date": "2024-08-30", "views": 2},
        {"date": "2024-08-31", "views": 28},
        {"date": "2024-09-01", "views": 6},
        {"date": "2024-09-02", "views": 16}
      ]
    },
    {
      "name": "data_0",
      "source": "source_0",
      "transform": [
        {"type": "formula", "expr": "toDate(datum[\"date\"])", "as": "date"},
        {
          "field": "date",
          "type": "timeunit",
          "units": ["year", "month", "date"],
          "as": ["yearmonthdate_date", "yearmonthdate_date_end"]
        },
        {
          "type": "stack",
          "groupby": ["yearmonthdate_date"],
          "field": "views",
          "sort": {"field": [], "order": []},
          "as": ["views_start", "views_end"],
          "offset": "zero"
        },
        {
          "type": "filter",
          "expr": "isValid(datum[\"views\"]) && isFinite(+datum[\"views\"])"
        },
        {"type": "extent", "field": "views", "signal": "extent"}
      ]
    }
  ],
  "signals": [
    {"name": "x_step", "value": 20},
    {
      "name": "width",
      "update": "bandspace(domain('x').length, 0.1, 0.05) * x_step"
    }
  ],
  "marks": [
    {
      "name": "marks", "zindex":0,
      "type": "rect",
      "style": ["bar"],
      "from": {"data": "data_0"},
      "encode": {
        "update": {
          "fill": {"signal": "gradient('color', [0,0], [0,1])"},
          "x": {"scale": "x", "field": "yearmonthdate_date"},
          "width": {"signal": "max(0.25, bandwidth('x'))"},
          "y": {"signal": "scale('y', extent[1])"},
          "y2": {"scale": "y", "field": "views_start"},
          
        }
      }
    },
    {
      "name": "marks2","zindex":1,
      "type": "rect",
      "style": ["bar"],
      "from": {"data": "data_0"},
      "encode": {
        "update": {
          "fill": {"signal": "'white'"},
          "x": {"scale": "x", "field": "yearmonthdate_date"},
          "width": {"signal": "max(0.25, bandwidth('x'))"},
          "y": {"signal": "scale('y', datum.views)"},
          "y2": {"signal": "scale('y', extent[1])"},
        
        }
      }
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "band",
      "domain": {"data": "data_0", "field": "yearmonthdate_date", "sort": true},
      "range": {"step": {"signal": "x_step"}},
      "paddingInner": 0.1,
      "paddingOuter": 0.05
    },
    {
      "name": "y",
      "type": "linear",
      "domain": {"data": "data_0", "fields": ["views_start", "views_end"]},
      "range": [{"signal": "height"}, 0],
      "nice": true,
      "zero": true
    },
    {
      "name": "color",
      "type": "sequential",
      "range": [
        "#002C41",
        "#35406F",
        "#834886",
        "#CE4D7C",
        "#FC6B55",
        "#FFA516"
      ]
    }
  ],
  "axes": [
    {
      "scale": "y",
      "orient": "left",
      "gridScale": "x",
      "grid": false,
      "tickCount": {"signal": "ceil(height/40)"},
      "domain": false,
      "labels": false,
      "aria": false,
      "maxExtent": 0,
      "minExtent": 0,
      "ticks": false
    },
    {
      "scale": "x",
      "orient": "bottom",
      "grid": false,
      "format": "%m/%d",
      "labelBound": true,
      "formatType": "time",
      "labelOverlap": true,
      "tickMinStep": {
        "signal": "datetime(2001, 0, 2, 0, 0, 0, 0) - datetime(2001, 0, 1, 0, 0, 0, 0)"
      },
      "zindex": 0
    },
    {
      "scale": "y",
      "orient": "left",
      "grid": false,
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "zindex": 0
    }
  ]
}