stackIndex

This determines which stack the series belongs to, given that stacking is enabled.

seriesSettings: {
    bar: {
        stackMode: 'normal'
    }
},
dataSeries: [
    {
        collectionAlias: 'Tokyo',
        stackIndex: 0,
        data: [5, 3, 4, 7, 2]
    },
    {
        collectionAlias: 'Tokyo1',
        stackIndex: 1,
        data: [2, 2, 3, 2, 1]
    },
    {
        collectionAlias: 'Tokyo2',
        stackIndex: 1,
        data: [3, 4, 4, 2, 5]
    }
]

This setting is demonstrated in the following example.