How to use the @nivo/radar.RadarDefaultProps.indexBy function in @nivo/radar

(3 layers and 4 dimensions).
        `,
        type: 'Array',
        required: true,
    },
    {
        key: 'indexBy',
        group: 'Base',
        help: 'Key to use to index the data.',
        description: `
            Key to use to index the data, this key
            must exist in each data item.
        `,
        type: 'string | number',
        required: false,
        defaultValue: defaults.indexBy,
    },
    {
        key: 'keys',
        group: 'Base',
        help: 'Keys to use to determine each serie.',
        description: `
            Keys to use to determine each serie.
            Those keys should exist in each data item.
        `,
        type: 'Array',
        required: false,
        defaultValue: defaults.keys,
    },
    {
        key: 'maxValue',
        help: 'Maximum value.',