v-concat.js

const grouped = _.groupBy(this.state.deepAnalysisGroupedBarChart, 'color')
this.state.deepAnalysisMaxValue = max.value

const _encoding = {
    x: {
        field: 'value',
        type: 'quantitative',
        scale: {
            domain: [0, max.value]
        }
    },
    y: {
        field: 'label',
        type: 'nominal',
        sort: {
            field: 'value'
        },
        axis: {
            title: null
        }
    },
    color: {
        field: 'label',
        type: 'nominal',
        scale: { range: { scheme: 'category20c' } }
    }
}

// Grouped bar chart using vconcat
this.state.deepAnalysisBarChartSpec = {
    $schema: 'https://vega.github.io/schema/vega-lite/v3.json',
    vconcat: _.keys(grouped).map(k => {
        let encoding = _cloneDeep(_encoding)
        encoding.y.axis.title = k
        return {
            data: { values: grouped[k] },
            mark: 'bar',
            encoding
        }
    })
}