# Pareto Chart

> A Pareto chart combines sorted bars with a cumulative percentage line to show which categories contribute most of the total.

A Pareto chart combines sorted bars with a cumulative percentage line to show which categories contribute most of the total. It answers 80/20 questions like "which customers drive most of our revenue?" at a glance.

<!-- TODO: add a screenshot of the rendered chart here -->

```aml
CustomChartDef pareto_chart {
  label: 'Pareto Chart'
  description: "A Pareto chart combines sorted bars with a cumulative percentage line to show which categories contribute most of the total."
  fields {
    field category {
      type: 'dimension'
      label: 'Category'
    }
    field value {
      type: 'measure'
      label: 'Value'
    }
  }
  options {
    option bar_color {
      type: 'color-picker'
      label: 'Bar Color'
      default_value: '#255dd4'
    }
    option line_color {
      type: 'color-picker'
      label: 'Cumulative Line Color'
      default_value: '#e5484d'
    }
    option show_threshold {
      type: 'toggle'
      label: 'Show 80% threshold line'
      default_value: true
    }
    option threshold {
      type: 'number-input'
      label: 'Threshold (0 to 1)'
      default_value: 0.8
    }
  }
  template: @vgl
  {
    "data": {"values": @{values}},
    "transform": [
      {
        "sort": [{"field": @{fields.value.name}, "order": "descending"}],
        "window": [{"op": "sum", "field": @{fields.value.name}, "as": "cumulative_sum"}],
        "frame": [null, 0]
      },
      {
        "joinaggregate": [{"op": "sum", "field": @{fields.value.name}, "as": "grand_total"}]
      },
      {
        "calculate": "datum.cumulative_sum / datum.grand_total",
        "as": "cumulative_percent"
      },
      {
        "calculate": "datum['@{fields.value.name}'] / datum.grand_total",
        "as": "item_share"
      },
      {
        "joinaggregate": [{"op": "min", "field": @{fields.value.name}, "as": "min_value"}]
      },
      {
        "calculate": "datum['@{fields.value.name}'] === datum.min_value ? (format(@{options.threshold.value}, '.0%') + ' of total') : ''",
        "as": "threshold_label"
      }
    ],
    "encoding": {
      "x": {
        "field": @{fields.category.name},
        "type": "nominal",
        "sort": {"field": @{fields.value.name}, "order": "descending"},
        "title": null,
        "scale": {"paddingInner": 0.25},
        "axis": {
          "labelOverlap": true,
          "domain": false,
          "ticks": false,
          "grid": false,
          "labelPadding": 8
        }
      }
    },
    "layer": [
      {
        "mark": {
          "type": "bar",
          "color": @{options.bar_color.value}
        },
        "encoding": {
          "y": {
            "field": @{fields.value.name},
            "type": "quantitative",
            "title": null,
            "axis": {
              "format": @{fields.value.format},
              "formatType": "holisticsFormat",
              "domain": false,
              "tickColor": "#E5E7EB",
              "grid": true,
              "gridColor": "#F3F4F6",
              "gridOpacity": 1
            }
          },
          "tooltip": [
            {"field": @{fields.category.name}, "type": "nominal", "title": "Category"},
            {"field": @{fields.value.name}, "type": "quantitative", "title": "Value", "format": @{fields.value.format}, "formatType": "holisticsFormat"},
            {"field": "item_share", "type": "quantitative", "title": "Share of Total", "format": ".1%"},
            {"field": "cumulative_percent", "type": "quantitative", "title": "Cumulative", "format": ".1%"}
          ]
        }
      },
      {
        "layer": [
      {
        "mark": {
          "type": "line",
          "point": {"filled": true, "size": 50, "fill": @{options.line_color.value}, "stroke": "white", "strokeWidth": 1},
          "color": @{options.line_color.value}
        },
        "encoding": {
          "y": {
            "field": "cumulative_percent",
            "type": "quantitative",
            "axis": {
              "format": ".0%",
              "title": "Cumulative %",
              "orient": "right",
              "titleColor": @{options.line_color.value},
              "domain": false,
              "tickColor": "#E5E7EB",
              "grid": false
            },
            "scale": {"domain": [0, 1]}
          },
          "tooltip": [
            {"field": @{fields.category.name}, "type": "nominal", "title": "Category"},
            {"field": "cumulative_percent", "type": "quantitative", "title": "Cumulative", "format": ".1%"}
          ]
        }
      },
      {
        "mark": {
          "type": "rule",
          "strokeDash": [4, 4],
          "color": "#9ba1a6",
          "opacity": {"expr": "@{options.show_threshold.value} ? 1 : 0"}
        },
        "encoding": {
          "x": null,
          "y": {"datum": @{options.threshold.value}, "type": "quantitative"}
        }
      },
      {
        "mark": {
          "type": "text",
          "align": "right",
          "baseline": "bottom",
          "dx": 6,
          "dy": -5,
          "fontSize": 10,
          "color": "#9ba1a6",
          "opacity": {"expr": "@{options.show_threshold.value} ? 1 : 0"}
        },
        "encoding": {
          "y": {"datum": @{options.threshold.value}, "type": "quantitative"},
          "text": {"field": "threshold_label"}
        }
      }
        ]
      }
    ],
    "resolve": {"scale": {"y": "independent"}},
    "config": {
      "background": null,
      "view": {
        "stroke": null
      },
      "axis": {
        "labelFontSize": 12,
        "titleFontSize": 12,
        "labelFontWeight": 400,
        "titleFontWeight": 500
      },
      "legend": {
        "labelFontSize": 12,
        "titleFontSize": 12,
        "labelFontWeight": 400,
        "symbolStrokeWidth": 0
      },
      "bar": {
        "cornerRadius": 2
      }
    }
  }
  ;;
}
```

<!-- TODO: add the View on GitHub footer link once the template lands in
     https://github.com/holistics/custom-chart-library -->