altair.expr#

class altair.expr(expr)#

Utility providing constants and classmethods to construct expressions.

Expressions can be used to write basic formulas that enable custom interactions.

Alternatively, an inline expression may be defined via expr().

Parameters:

expr: str: A vega expression string.

Returns:

ExprRef

Examples

>>> import altair as alt

>>> bind_range = alt.binding_range(min=100, max=300, name="Slider value:  ")
>>> param_width = alt.param(bind=bind_range, name="param_width")
>>> param_color = alt.param(
...     expr=alt.expr.if_(param_width < 200, "red", "black"),
...     name="param_color",
... )
>>> y = alt.Y("yval").axis(titleColor=param_color)

>>> y
Y({
  axis: {'titleColor': Parameter('param_color', VariableParameter({
    expr: if((param_width < 200),'red','black'),
    name: 'param_color'
  }))},
  shorthand: 'yval'
})

__init__(expr=Undefined, **kwds)#

Methods

`__init__`([expr])
`abs`(value, /)	Returns the absolute value of `value`.
`acos`(value, /)	Trigonometric arccosine.
`asin`(value, /)	Trigonometric arcsine.
`atan`(value, /)	Trigonometric arctangent.
`atan2`(dy, dx, /)	Returns the arctangent of dy / dx.
`bandspace`(count[, paddingInner, paddingOuter])	Returns the number of steps needed within a band scale, based on the `count` of domain elements and the inner and outer padding values.
`bandwidth`(name[, group])	Returns the current band width for the named band scale transform, or zero if the scale is not found or is not a band scale.
`ceil`(value, /)	Rounds `value` to the nearest integer of equal or greater value.
`clamp`(value, min, max, /)	Restricts `value` to be between the specified `min` and `max`.
`clampRange`(range, min, max, /)	Clamps a two-element `range` array in a span-preserving manner.
`containerSize`()	Returns the current CSS box size (`[el.clientWidth, el.clientHeight]`) of the parent DOM element that contains the Vega view.
`contrast`(specifier1, specifier2, /)	Returns the contrast ratio between the input color specifiers as a float between 1 and 21.
`copy`(name[, group])	Returns a copy (a new cloned instance) of the named scale transform of projection, or `undefined` if no scale or projection is found.
`cos`(value, /)	Trigonometric cosine.
`cumulativeLogNormal`(value[, mean, stdev])	Returns the value of the cumulative distribution function at the given input domain `value` for a log-normal distribution with specified log `mean` and log standard deviation `stdev`.
`cumulativeNormal`(value[, mean, stdev])	Returns the value of the cumulative distribution function at the given input domain `value` for a normal distribution with specified `mean` and standard deviation `stdev`.
`cumulativeUniform`(value[, min, max])	Returns the value of the cumulative distribution function at the given input domain `value` for a uniform distribution over the interval [`min`, `max`).
`data`(name, /)	Returns the array of data objects for the Vega data set with the given `name`.
`date`(datetime, /)	Returns the day of the month for the given `datetime` value, in local time.
`datetime`(year, month[, day, hour, min, sec, ...])	Returns a new `Date` instance.
`day`(datetime, /)	Returns the day of the week for the given `datetime` value, in local time.
`dayAbbrevFormat`(day, /)	Formats a (0-6) weekday number as an abbreviated week day name, according to the current locale.
`dayFormat`(day, /)	Formats a (0-6) weekday number as a full week day name, according to the current locale.
`dayofyear`(datetime, /)	Returns the one-based day of the year for the given `datetime` value, in local time.
`debug`(value1[, value2])	Logs a debugging message and returns the last argument.
`densityLogNormal`(value[, mean, stdev])	Returns the value of the probability density function at the given input domain `value`, for a log-normal distribution with specified log `mean` and log standard deviation `stdev`.
`densityNormal`(value[, mean, stdev])	Returns the value of the probability density function at the given input domain `value`, for a normal distribution with specified `mean` and standard deviation `stdev`.
`densityUniform`(value[, min, max])	Returns the value of the probability density function at the given input domain `value`, for a uniform distribution over the interval [`min`, `max`).
`domain`(name[, group])	Returns the scale domain array for the named scale transform, or an empty array if the scale is not found.
`exp`(exponent, /)	Returns the value of e raised to the provided `exponent`.
`extent`(array, /)	Returns a new [min, max] array with the minimum and maximum values of the input array, ignoring `null`, `undefined`, and `NaN` values.
`floor`(value, /)	Rounds `value` to the nearest integer of equal or lower value.
`format`(value, specifier, /)	Formats a numeric `value` as a string.
`from_dict`(dct[, validate])	Construct class from a dictionary representation.
`from_json`(json_string[, validate])	Instantiate the object from a valid JSON string.
`geoArea`(projection, feature[, group])	Returns the projected planar area (typically in square pixels) of a GeoJSON `feature` according to the named `projection`.
`geoBounds`(projection, feature[, group])	Returns the projected planar bounding box (typically in pixels) for the specified GeoJSON `feature`, according to the named `projection`.
`geoCentroid`(projection, feature[, group])	Returns the projected planar centroid (typically in pixels) for the specified GeoJSON `feature`, according to the named `projection`.
`geoScale`(projection[, group])	Returns the scale value for the named `projection`.
`gradient`(scale, p0, p1[, count])	Returns a linear color gradient for the `scale` (whose range must be a continuous color scheme) and starting and ending points `p0` and `p1`, each an [x, y] array.
`group`([name])	Returns the scenegraph group mark item in which the current event has occurred.
`hcl`(*args)	Constructs a new HCL (hue, chroma, luminance) color.
`hours`(datetime, /)	Returns the hours component for the given `datetime` value, in local time.
`hsl`(*args)	Constructs a new HSL color.
`hypot`(value, /)	Returns the square root of the sum of squares of its arguments.
`if_`(test, thenValue, elseValue, /)	If `test` is truthy, returns `thenValue`.
`inScope`(item, /)	Returns true if the given scenegraph `item` is a descendant of the group mark in which the event handler was defined, false otherwise.
`indata`(name, field, value, /)	Tests if the data set with a given `name` contains a datum with a `field` value that matches the input `value`.
`indexof`(array, value, /)	Returns the first index of `value` in the input `array`.
`info`(value1[, value2])	Logs an informative message and returns the last argument.
`inrange`(value, range, /)	Tests whether `value` lies within (or is equal to either) the first and last values of the `range` array.
`invert`(name, value[, group])	Inverts the named scale transform (or projection) for the specified `value`.
`isArray`(value, /)	Returns true if `value` is an array, false otherwise.
`isBoolean`(value, /)	Returns true if `value` is a boolean (`true` or `false`), false otherwise.
`isDate`(value, /)	Returns true if `value` is a Date object, false otherwise.
`isDefined`(value, /)	Returns true if `value` is a defined value, false if `value` equals `undefined`.
`isFinite`(value, /)	Returns true if `value` is a finite number.
`isNaN`(value, /)	Returns true if `value` is not a number.
`isNumber`(value, /)	Returns true if `value` is a number, false otherwise.
`isObject`(value, /)	Returns true if `value` is an object (including arrays and Dates), false otherwise.
`isRegExp`(value, /)	Returns true if `value` is a RegExp (regular expression) object, false otherwise.
`isString`(value, /)	Returns true if `value` is a string, false otherwise.
`isValid`(value, /)	Returns true if `value` is not `null`, `undefined`, or `NaN`, false otherwise.
`item`()	Returns the current scenegraph item that is the target of the event.
`join`(array[, separator])	Returns a new string by concatenating all of the elements of the input `array`, separated by commas or a specified `separator` string.
`lab`(*args)	Constructs a new CIE LAB color.
`lastindexof`(array, value, /)	Returns the last index of `value` in the input `array`.
`length`(array, /)	Returns the length of the input `array`.
`lerp`(array, fraction, /)	Returns the linearly interpolated value between the first and last entries in the `array` for the provided interpolation `fraction` (typically between 0 and 1).
`log`(value, /)	Returns the natural logarithm of `value`.
`lower`(string, /)	Transforms `string` to lower-case letters.
`luminance`(specifier, /)	Returns the luminance for the given color `specifier` (compatible with d3-color's rgb function).
`max`(value1, value2, *args)	Returns the maximum argument value.
`merge`(object1[, object2])	Merges the input objects `object1`, `object2`, etc into a new output object.
`milliseconds`(datetime, /)	Returns the milliseconds component for the given `datetime` value, in local time.
`min`(value1, value2, *args)	Returns the minimum argument value.
`minutes`(datetime, /)	Returns the minutes component for the given `datetime` value, in local time.
`month`(datetime, /)	Returns the (zero-based) month for the given `datetime` value, in local time.
`monthAbbrevFormat`(month, /)	Formats a (zero-based) `month` number as an abbreviated month name, according to the current locale.
`monthFormat`(month, /)	Formats a (zero-based) `month` number as a full month name, according to the current locale.
`now`()	Returns the timestamp for the current time.
`pad`(string, length[, character, align])	Pads a `string` value with repeated instances of a `character` up to a specified `length`.
`panLinear`(domain, delta, /)	Given a linear scale `domain` array with numeric or datetime values, returns a new two-element domain array that is the result of panning the domain by a fractional `delta`.
`panLog`(domain, delta, /)	Given a log scale `domain` array with numeric or datetime values, returns a new two-element domain array that is the result of panning the domain by a fractional `delta`.
`panPow`(domain, delta, exponent, /)	Given a power scale `domain` array with numeric or datetime values and the given `exponent`, returns a new two-element domain array that is the result of panning the domain by a fractional `delta`.
`panSymlog`(domain, delta, constant, /)	Given a symmetric log scale `domain` array with numeric or datetime values parameterized by the given `constant`, returns a new two-element domain array that is the result of panning the domain by a fractional `delta`.
`parseFloat`(string, /)	Parses the input `string` to a floating-point value.
`parseInt`(string, /)	Parses the input `string` to an integer value.
`peek`(array, /)	Returns the last element in the input `array`.
`pinchAngle`(event, /)	Returns the angle of the line connecting the first two touch points of a multi-touch event.
`pinchDistance`(event, /)	Returns the pixel distance between the first two touch points of a multi-touch event.
`pluck`(array, field, /)	Retrieves the value for the specified `field` from a given `array` of objects.
`pow`(value, exponent, /)	Returns `value` raised to the given `exponent`.
`quantileLogNormal`(probability[, mean, stdev])	Returns the quantile value (the inverse of the cumulative distribution function) for the given input `probability`, for a log-normal distribution with specified log `mean` and log standard deviation `stdev`.
`quantileNormal`(probability[, mean, stdev])	Returns the quantile value (the inverse of the cumulative distribution function) for the given input `probability`, for a normal distribution with specified `mean` and standard deviation `stdev`.
`quantileUniform`(probability[, min, max])	Returns the quantile value (the inverse of the cumulative distribution function) for the given input `probability`, for a uniform distribution over the interval [`min`, `max`).
`quarter`(datetime, /)	Returns the quarter of the year (0-3) for the given `datetime` value, in local time.
`random`()	Returns a pseudo-random number in the range [0,1).
`range`(name[, group])	Returns the scale range array for the named scale transform, or an empty array if the scale is not found.
`regexp`(pattern[, flags])	Creates a regular expression instance from an input `pattern` string and optional `flags`.
`replace`(string, pattern, replacement, /)	Returns a new string with some or all matches of `pattern` replaced by a `replacement` string.
`resolve_references`([schema])	Resolve references in the context of this object's schema or root schema.
`reverse`(array, /)	Returns a new array with elements in a reverse order of the input `array`.
`rgb`(*args)	Constructs a new RGB color.
`round`(value, /)	Rounds `value` to the nearest integer.
`sampleLogNormal`([mean, stdev])	Returns a sample from a univariate log-normal probability distribution with specified log `mean` and log standard deviation `stdev`.
`sampleNormal`([mean, stdev])	Returns a sample from a univariate normal (Gaussian) probability distribution with specified `mean` and standard deviation `stdev`.
`sampleUniform`([min, max])	Returns a sample from a univariate continuous uniform probability distribution over the interval [`min`, `max`).
`scale`(name, value[, group])	Applies the named scale transform (or projection) to the specified `value`.
`screen`()	Returns the window.screen object, or `{}` if Vega is not running in a browser environment.
`seconds`(datetime, /)	Returns the seconds component for the given `datetime` value, in local time.
`sequence`(*args)	Returns an array containing an arithmetic sequence of numbers.
`sin`(value, /)	Trigonometric sine.
`slice`(array, start[, end])	Returns a section of `array` between the `start` and `end` indices.
`span`(array, /)	Returns the span of `array`: the difference between the last and first elements, or array[array.length-1] - array[0].
`sqrt`(value, /)	Square root function.
`substring`(string, start[, end])	Returns a section of `string` between the `start` and `end` indices.
`tan`(value, /)	Trigonometric tangent.
`test`(regexp[, string])	Evaluates a regular expression `regexp` against the input `string`, returning `true` if the string matches the pattern, `false` otherwise.
`time`(datetime, /)	Returns the epoch-based timestamp for the given `datetime` value.
`timeFormat`(value, specifier, /)	Formats a datetime `value` (either a `Date` object or timestamp) as a string, according to the local time.
`timeOffset`(unit, date[, step])	Returns a new `Date` instance that offsets the given `date` by the specified time unit in the local timezone.
`timeParse`(string, specifier, /)	Parses a `string` value to a Date object, according to the local time.
`timeSequence`(unit, start, stop[, step])	Returns an array of `Date` instances from `start` (inclusive) to `stop` (exclusive), with each entry separated by the given time unit in the local timezone.
`timeUnitSpecifier`(units[, specifiers])	Returns a time format specifier string for the given time units.
`timezoneoffset`(datetime, /)	Returns the timezone offset from the local timezone to UTC for the given `datetime` value.
`toBoolean`(value, /)	Coerces the input `value` to a string.
`toDate`(value, /)	Coerces the input `value` to a Date instance.
`toNumber`(value, /)	Coerces the input `value` to a number.
`toString`(value, /)	Coerces the input `value` to a string.
`to_dict`([validate, ignore, context])	Return a dictionary representation of the object.
`to_json`([validate, indent, sort_keys, ...])	Emit the JSON representation for this object as a string.
`treeAncestors`(name, node, /)	For the hierarchy data set with the given `name`, returns the array of ancestors nodes, starting with the input `node`, then followed by each parent up to the root.
`treePath`(name, source, target, /)	For the hierarchy data set with the given `name`, returns the shortest path through from the `source` node id to the `target` node id.
`trim`(string, /)	Returns a trimmed string with preceding and trailing whitespace removed.
`truncate`(string, length[, align, ellipsis])	Truncates an input `string` to a target `length`.
`upper`(string, /)	Transforms `string` to upper-case letters.
`utc`(year, month[, day, hour, min, sec, millisec])	Returns a timestamp for the given UTC date.
`utcFormat`(value, specifier, /)	Formats a datetime `value` (either a `Date` object or timestamp) as a string, according to UTC time.
`utcOffset`(unit, date[, step])	Returns a new `Date` instance that offsets the given `date` by the specified time unit in UTC time.
`utcParse`(value, specifier, /)	Parses a string value to a Date object, according to UTC time.
`utcSequence`(unit, start, stop[, step])	Returns an array of `Date` instances from `start` (inclusive) to `stop` (exclusive), with each entry separated by the given time unit in UTC time.
`utcdate`(datetime, /)	Returns the day of the month for the given `datetime` value, in UTC time.
`utcday`(datetime, /)	Returns the day of the week for the given `datetime` value, in UTC time.
`utcdayofyear`(datetime, /)	Returns the one-based day of the year for the given `datetime` value, in UTC time.
`utchours`(datetime, /)	Returns the hours component for the given `datetime` value, in UTC time.
`utcmilliseconds`(datetime, /)	Returns the milliseconds component for the given `datetime` value, in UTC time.
`utcminutes`(datetime, /)	Returns the minutes component for the given `datetime` value, in UTC time.
`utcmonth`(datetime, /)	Returns the (zero-based) month for the given `datetime` value, in UTC time.
`utcquarter`(datetime, /)	Returns the quarter of the year (0-3) for the given `datetime` value, in UTC time.
`utcseconds`(datetime, /)	Returns the seconds component for the given `datetime` value, in UTC time.
`utcweek`(date, /)	Returns the week number of the year for the given datetime, in UTC time.
`utcyear`(datetime, /)	Returns the year for the given `datetime` value, in UTC time.
`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.
`warn`(value1[, value2])	Logs a warning message and returns the last argument.
`week`(date, /)	Returns the week number of the year for the given datetime, in local time.
`windowSize`()	Returns the current window size (`[window.innerWidth, window.innerHeight]`) or `[undefined, undefined]` if Vega is not running in a browser environment.
`x`([item])	Returns the x coordinate for the current event.
`xy`([item])	Returns the x- and y-coordinates for the current event as a two-element array.
`y`([item])	Returns the y coordinate for the current event.
`year`(datetime, /)	Returns the year for the given `datetime` value, in local time.
`zoomLinear`(domain, anchor, scaleFactor, /)	Given a linear scale `domain` array with numeric or datetime values, returns a new two-element domain array that is the result of zooming the domain by a `scaleFactor`, centered at the provided fractional `anchor`.
`zoomLog`(domain, anchor, scaleFactor, /)	Given a log scale `domain` array with numeric or datetime values, returns a new two-element domain array that is the result of zooming the domain by a `scaleFactor`, centered at the provided fractional `anchor`.
`zoomPow`(domain, anchor, scaleFactor, exponent, /)	Given a power scale `domain` array with numeric or datetime values and the given `exponent`, returns a new two-element domain array that is the result of zooming the domain by a `scaleFactor`, centered at the provided fractional `anchor`.
`zoomSymlog`(domain, anchor, scaleFactor, ...)	Given a symmetric log scale `domain` array with numeric or datetime values parameterized by the given `constant`, returns a new two-element domain array that is the result of zooming the domain by a `scaleFactor`, centered at the provided fractional `anchor`.