vega-lite - 将 domainMin 设置为数据中最大日期之前的 6 个月

Question

我有以下 Vega-Lite 图表:

Open the Chart in the Vega Editor

目前我设置的比例如下:

"scale": {"domainMin": "2021-06-01"}

但是，我真正想要的是 domainMin 自动计算为数据中 notification_date 字段中的最新日期之前 6 个月。我看过 aggregate和 expressions , 但还不是很清楚。

如何获取 notification_date 的最大值并从中减去 6 个月，然后在 "domainMin" 中使用它？

编辑:澄清一下，我不想过滤数据。我希望用户能够缩小或平移以查看初始 6 个月窗口之外的数据。我用 "scale": {"domainMin": "2021-06-01"} 得到了我想要的，但这很快就过时了。

Answer 1

我已经尝试将 params 和 expr 赋给 domainMin，但我无法通过 datum 使用 expr 中的数据字段。

我尝试的第二种方法适合您，在此您需要使用joinaggregate/calculate/filter 转换。您将手动收集最大年份和最大月份，然后使用它来过滤您的数据。

以下是修改后的配置或引用editor网址:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "width": "container",
  "height": "container",
  "config": {
    "group": {"fill": "#e5e5e5"},
    "arc": {"fill": "#2b2c39"},
    "area": {"fill": "#2b2c39"},
    "line": {"stroke": "#2b2c39"},
    "path": {"stroke": "#2b2c39"},
    "rect": {"fill": "#2b2c39"},
    "shape": {"stroke": "#2b2c39"},
    "symbol": {"fill": "#2b2c39"},
    "range": {
      "category": [
        "#2283a2",
        "#003e6a",
        "#a1ce5e",
        "#FDBE13",
        "#F2727E",
        "#EA3F3F",
        "#25A9E0",
        "#F97A08",
        "#41BFB8",
        "#518DCA",
        "#9460A8",
        "#6F7D84",
        "#D1DCA5"
      ]
    }
  },
  "title": "South Western Sydney Cumulative and Daily COVID-19 Cases by LGA",
  "data": {
    "url": "https://davidwales.github.io/nsw-covid-19-data/confirmed_cases_table1_location.csv"
  },
  "transform": [
    {
      "filter": {
        "and": [
          {"field": "lhd_2010_name", "equal": "South Western Sydney"},
          {"not": {"field": "lga_name19", "equal": "Penrith"}}
        ]
      }
    },
    {"calculate": "utcyear(datum.notification_date)", "as": "yearNumber"},
    {"calculate": "utcmonth(datum.notification_date)", "as": "monthNumber"},
    {
      "window": [
        {"op": "count", "field": "notification_date", "as": "cumulative_count"}
      ],
      "frame": [null, 0]
    },
    {
      "joinaggregate": [
        {"field": "monthNumber", "op": "max", "as": "max_month_count"},
        {"field": "yearNumber", "op": "max", "as": "max_year"}
      ]
    },
    {"calculate": "abs(datum.max_month_count-6)", "as": "min_month_count"},
    {
      "filter": "datum.min_month_count < datum.monthNumber && datum.max_year === datum.yearNumber"
    }
  ],
  "layer": [
    {
      "selection": {
        "date": {"type": "interval", "bind": "scales", "encodings": ["x"]}
      },
      "mark": {"type": "bar", "tooltip": true},
      "encoding": {
        "x": {
          "timeUnit": "yearmonthdate",
          "field": "notification_date",
          "type": "temporal",
          "title": "Date"
        },
        "color": {
          "field": "lga_name19",
          "type": "nominal",
          "title": "LGA",
          "legend": {"orient": "top", "columns": 4}
        },
        "y": {
          "aggregate": "count",
          "field": "lga_name19",
          "type": "quantitative",
          "title": "Cases",
          "axis": {"title": "Daily Cases by SWS LGA"}
        }
      }
    },
    {
      "mark": "line",
      "encoding": {
        "x": {
          "timeUnit": "yearmonthdate",
          "field": "notification_date",
          "title": "Date",
          "type": "temporal"
        },
        "y": {
          "aggregate": "max",
          "field": "cumulative_count",
          "type": "quantitative",
          "axis": {"title": "Cumulative Cases"}
        }
      }
    }
  ],
  "resolve": {"scale": {"y": "independent"}}
}