DotBin Transform
The dotbin transform ≥ 5.7 calculates bin positions for stacking dots in a dot plot. This transform implements the “dot density” algorithm of Wilkinson’s “Dot Plots”, The American Statistician, 1999. If a groupby parameter is provided, bins are computed separately per group. After computing dot positions, the stack transform can be used to compute stacked dot positions.
Transform Parameters
| Property | Type | Description |
|---|---|---|
| field | Field | Required. The data field to bin. |
| groupby | Field[ ] | The data fields to group by. If not specified, a single group containing all data objects will be used. |
| step | Number | The step size (bin width) within which dots should be stacked. Defaults to 1/30 of the extent of the data field. |
| smooth | Boolean | A boolean flag indicating if dot density stacks should be smoothed to reduce variance (default false). |
| signal | String | If defined, binds the computed binning parameters (an object with start, stop and step properties) to a signal with the given name. |
| as | String | The output fields for the sample value and associated probability. The default is "bin". |
Usage
This example computes dot plot locations for the value field with default step parameter:
[
{"type": "dotbin", "field": "amount", "as": "bin", "signal": "dotbins"},
{"type": "stack", "field": "amount", "groupby": ["bin"], "as": ["y0", "y1"]}
]
The calculated start, stop, and step values are bound to a new signal named dotbins. A dot plot can be constructed using a symbol mark with the x-coordinate determined by a linear scale over the bin field, and y-coordinate set to the mid-point between y0 and y1. The y-axis scale and the size of the symbol mark depend on the x-axis scale and the output dotbins.step value. For more, see the dot-plot and quantile-dot-plot examples.