[vega-lite] Line Chart of radian scale functions using sequence/fold/labelExpr (vega-lite v4.0)

Vega-lite-transform-legends.json

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "Plots radian scale functions using sequence/fold/labelExpr.",
  "width": 300,
  "height": 150,
  "data": {
    "sequence": {
      "start": -1,
      "stop": 1.1,
      "step": 0.1,
      "as": "Normalized Frequency"
    }
  },
  "transform": [
    {
      "calculate": "datum['Normalized Frequency'] * PI",
      "as": "Radian"
    },
    {
      "calculate": "sin(datum['Radian'])",
      "as": "sin(x)"
    },
    {
      "calculate": "cos(datum['Radian'])",
      "as": "cos(x)"
    },
    {
      "fold": ["sin(x)", "cos(x)"],
      "as": ["Expression", "Value"]
    }
  ],
  "mark": "line",
  "encoding": {
    "x": {
      "field": "Normalized Frequency",
      "type": "quantitative",
      "axis": {
        "title": "x",
        "format": ".2f",
        "offset": -75,
        "titleAngle": 0,
        "titleX": -10,
        "titleY": -5,
        "tickCount": 4,
        "labelExpr": "datum.label + 'π'"
      }
    },
    "y": {
      "field": "Value",
      "type": "quantitative",
      "axis": {
        "title": "y",
        "format": ".1f",
        "offset": -150,
        "titleAngle": 0,
        "titleX": 0,
        "titleY": -10
      }
    },
    "color": {
      "field": "Expression",
      "type": "nominal",
      "legend": {
        "title": "Expression"
      }
    }
  }
}

Vega-transform-legends.json

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "Plots radian scale functions using sequence/fold/labelExpr.",
  "autosize": "pad",
  "padding": 5,
  "width": 300,
  "height": 150,
  "style": "cell",
  "data": [
    {
      "name": "source_0",
      "transform": [
        {
          "type": "sequence",
          "start": -1,
          "stop": 1.1,
          "step": 0.1,
          "as": "Normalized Frequency"
        },
        {
          "type": "formula",
          "expr": "datum['Normalized Frequency'] * PI",
          "as": "Radian"
        },
        {"type": "formula", "expr": "sin(datum['Radian'])", "as": "sin(x)"},
        {"type": "formula", "expr": "cos(datum['Radian'])", "as": "cos(x)"},
        {
          "type": "fold",
          "fields": ["sin(x)", "cos(x)"],
          "as": ["Expression", "Value"]
        }
      ]
    }
  ],
  "marks": [
    {
      "name": "pathgroup",
      "type": "group",
      "from": {
        "facet": {
          "name": "faceted_path_main",
          "data": "source_0",
          "groupby": ["Expression"]
        }
      },
      "encode": {
        "update": {
          "width": {"field": {"group": "width"}},
          "height": {"field": {"group": "height"}}
        }
      },
      "marks": [
        {
          "name": "marks",
          "type": "line",
          "style": ["line"],
          "sort": {"field": "datum[\"Normalized Frequency\"]"},
          "from": {"data": "faceted_path_main"},
          "encode": {
            "update": {
              "stroke": {"scale": "color", "field": "Expression"},
              "x": {"scale": "x", "field": "Normalized Frequency"},
              "y": {"scale": "y", "field": "Value"},
              "defined": {
                "signal": "datum[\"Normalized Frequency\"] !== null && isFinite(datum[\"Normalized Frequency\"]) && datum[\"Value\"] !== null && isFinite(datum[\"Value\"])"
              }
            }
          }
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "linear",
      "domain": {"data": "source_0", "field": "Normalized Frequency"},
      "range": [0, {"signal": "width"}],
      "nice": true,
      "zero": false
    },
    {
      "name": "y",
      "type": "linear",
      "domain": {"data": "source_0", "field": "Value"},
      "range": [{"signal": "height"}, 0],
      "nice": true,
      "zero": true
    },
    {
      "name": "color",
      "type": "ordinal",
      "domain": {"data": "source_0", "field": "Expression", "sort": true},
      "range": "category"
    }
  ],
  "axes": [
    {
      "scale": "x",
      "orient": "bottom",
      "tickCount": 4,
      "gridScale": "y",
      "grid": true,
      "domain": false,
      "labels": false,
      "maxExtent": 0,
      "minExtent": 0,
      "ticks": false,
      "zindex": 0
    },
    {
      "scale": "y",
      "orient": "left",
      "gridScale": "x",
      "grid": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "domain": false,
      "labels": false,
      "maxExtent": 0,
      "minExtent": 0,
      "ticks": false,
      "zindex": 0
    },
    {
      "scale": "x",
      "orient": "bottom",
      "grid": false,
      "title": "x",
      "format": ".2f",
      "offset": -75,
      "tickCount": 4,
      "titleAngle": 0,
      "titleX": -10,
      "titleY": -5,
      "labelFlush": true,
      "labelOverlap": true,
      "encode": {
        "labels": {"update": {"text": {"signal": "datum.label + 'π'"}}}
      },
      "zindex": 0
    },
    {
      "scale": "y",
      "orient": "left",
      "grid": false,
      "title": "y",
      "format": ".1f",
      "offset": -150,
      "titleAngle": 0,
      "titleX": 0,
      "titleY": -10,
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "zindex": 0
    }
  ],
  "legends": [
    {
      "title": "Expression",
      "stroke": "color",
      "gradientLength": {"signal": "clamp(height, 64, 200)"},
      "symbolType": "stroke"
    }
  ]
}

Enables to run by Vega Editor: https://vega.github.io/editor/#/custom/vega-lite
Original: https://vega.github.io/vega-lite/docs/data.html#sequence