interaction8.vl

{
    "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
    "data": {
        "url": "https://vega.github.io/vega-lite/data/seattle-weather.csv"
    },
    "encoding": {
        "y": {
            "aggregate": "mean",
            "field": "precipitation",
            "type": "quantitative"
        }
    },
    "layer": [
        {
            "encoding": {
                "opacity": {
                    "condition": {
                        "selection": "myBrush",
                        "value": 1
                    },
                    "value": 0.7
                },
                "x": {
                    "field": "date",
                    "timeUnit": "month",
                    "type": "ordinal"
                }
            },
            "mark": "bar",
            "selection": {
                "myBrush": {
                    "encodings": [
                        "x"
                    ],
                    "type": "interval"
                }
            }
        },
        {
            "description": "Drag over bars to update selection average",
            "encoding": {
                "color": {
                    "value": "firebrick"
                },
                "size": {
                    "value": 3
                }
            },
            "mark": "rule",
            "transform": [
                {
                    "filter": {
                        "selection": "myBrush"
                    }
                }
            ]
        }
    ]
}