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.
atob(string, /)	Decodes an ASCII string that was encoded with Base64.
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.
btoa(string, /)	Creates a Base64-encoded ASCII string.
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.
sort(array, /)	Sorts the array in natural order using ascending from Vega Utils.
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.