class altair.StringFieldDef(aggregate=Undefined, band=Undefined, bin=Undefined, field=Undefined, format=Undefined, formatType=Undefined, labelExpr=Undefined, timeUnit=Undefined, title=Undefined, type=Undefined, **kwds)

StringFieldDef schema wrapper



Aggregation function for the field (e.g., "mean", "sum", "median", "min", "max", "count" ).

Default value: undefined (None)

See also: aggregate documentation.


For rect-based marks ( rect, bar, and image ), mark size relative to bandwidth of band scales, bins or time units. If set to 1, the mark size is set to the bandwidth, the bin interval, or the time unit interval. If set to 0.5, the mark size is half of the bandwidth or the time unit interval.

For other marks, relative position on a band of a stacked, binned, time unit or band scale. If set to 0, the marks will be positioned at the beginning of the band. If set to 0.5, the marks will be positioned in the middle of the band.

binanyOf(boolean, BinParams, string, None)

A flag for binning a quantitative field, an object defining binning parameters, or indicating that the data for x or y channel are binned before they are imported into Vega-Lite ( "binned" ).

If true, default binning parameters will be applied.

If "binned", this indicates that the data for the x (or y ) channel are already binned. You can map the bin-start field to x (or y ) and the bin-end field to x2 (or y2 ). The scale and axis will be formatted similar to binning in Vega-Lite. To adjust the axis ticks based on the bin step, you can also set the axis’s tickMinStep property.

Default value: false

See also: bin documentation.


Required. A string defining the name of the field from which to pull a data value or an object defining iterated values from the repeat operator.

See also: field documentation.

Notes: 1) Dots ( . ) and brackets ( [ and ] ) can be used to access nested objects (e.g., "field": "" and "field": "foo['bar']" ). If field names contain dots or brackets but are not nested, you can use \ to escape dots and brackets (e.g., "a\.b" and "a\[0\]" ). See more details about escaping in the field documentation. 2) field is not required if aggregate is count.

formatanyOf(string, Dictunknown)

When used with the default "number" and "time" format type, the text formatting pattern for labels of guides (axes, legends, headers) and text marks.

See the format documentation for more examples.

When used with a custom formatType, this value will be passed as format alongside datum.value to the registered function.

Default value: Derived from numberFormat config for number format and from timeFormat config for time format.


The format type for labels. One of "number", "time", or a registered custom format type.

Default value: - "time" for temporal fields and ordinal and nominal fields with timeUnit. - "number" for quantitative fields as well as ordinal and nominal fields without timeUnit.


Vega expression for customizing labels text.

Note: The label text and value can be assessed via the label and value properties of the axis’s backing datum object.

timeUnitanyOf(TimeUnit, TimeUnitParams)

Time unit (e.g., year, yearmonth, month, hours ) for a temporal field. or a temporal field that gets casted as ordinal.

Default value: undefined (None)

See also: timeUnit documentation.

titleanyOf(Text, None)

A title for the field. If null, the title will be removed.

Default value: derived from the field’s name and transformation function ( aggregate, bin and timeUnit ). If the field has an aggregate function, the function is displayed as part of the title (e.g., "Sum of Profit" ). If the field is binned or has a time unit applied, the applied function is shown in parentheses (e.g., "Profit (binned)", "Transaction Date (year-month)" ). Otherwise, the title is simply the field name.

Notes :

1) You can customize the default field title format by providing the fieldTitle property in the config or fieldTitle function via the compile function’s options.

2) If both field definition’s title and axis, header, or legend title are defined, axis/header/legend title will be used.


The type of measurement ( "quantitative", "temporal", "ordinal", or "nominal" ) for the encoded field or constant value ( datum ). It can also be a "geojson" type for encoding ‘geoshape’.

Vega-Lite automatically infers data types in many cases as discussed below. However, type is required for a field if: (1) the field is not nominal and the field encoding has no specified aggregate (except argmin and argmax ), bin, scale type, custom sort order, nor timeUnit or (2) if you wish to use an ordinal scale for a field with bin or timeUnit.

Default value:

1) For a data field, "nominal" is the default data type unless the field encoding has aggregate, channel, bin, scale type, sort, or timeUnit that satisfies the following criteria: - "quantitative" is the default type if (1) the encoded field contains bin or aggregate except "argmin" and "argmax", (2) the encoding channel is latitude or longitude channel or (3) if the specified scale type is a quantitative scale. - "temporal" is the default type if (1) the encoded field contains timeUnit or (2) the specified scale type is a time or utc scale - ordinal"" is the default type if (1) the encoded field contains a custom sort order, (2) the specified scale type is an ordinal/point/band scale, or (3) the encoding channel is order.

2) For a constant value in data domain ( datum ): - "quantitative" if the datum is a number - "nominal" if the datum is a string - "temporal" if the datum is a date time object

Note: - Data type describes the semantics of the data rather than the primitive data types (number, string, etc.). The same primitive data type can have different types of measurement. For example, numeric data can represent quantitative, ordinal, or nominal data. - Data values for a temporal field can be either a date-time string (e.g., "2015-03-07 12:32:17", "17:01", "2015-03-16". "2015" ) or a timestamp number (e.g., 1552199579097 ). - When using with bin, the type property can be either "quantitative" (for using a linear bin scale) or “ordinal” (for using an ordinal bin scale). - When using with timeUnit, the type property can be either "temporal" (default, for using a temporal scale) or “ordinal” (for using an ordinal scale). - When using with aggregate, the type property refers to the post-aggregation data type. For example, we can calculate count distinct of a categorical field "cat" using {"aggregate": "distinct", "field": "cat"}. The "type" of the aggregate output is "quantitative". - Secondary channels (e.g., x2, y2, xError, yError ) do not have type as they must have exactly the same type as their primary channels (e.g., x, y ).

See also: type documentation.

__init__(aggregate=Undefined, band=Undefined, bin=Undefined, field=Undefined, format=Undefined, formatType=Undefined, labelExpr=Undefined, timeUnit=Undefined, title=Undefined, type=Undefined, **kwds)


__init__([aggregate, band, bin, field, ...])

copy([deep, ignore])

Return a copy of the object

from_dict(dct[, validate, _wrapper_classes])

Construct class from a dictionary representation

from_json(json_string[, validate])

Instantiate the object from a valid JSON string


Resolve references in the context of this object's schema or root schema.

to_dict([validate, ignore, context])

Return a dictionary representation of the object

to_json([validate, ignore, context, indent, ...])

Emit the JSON representation for this object as a string.

validate(instance[, schema])

Validate the instance against the class schema in the context of the rootschema.

validate_property(name, value[, schema])

Validate a property against property schema in the context of the rootschema