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namespaceChart Scales6 functions

datumhue.chart.scale

Construct shared scales (data → pixels / data → color) for chart marks. A scale exists independently of any plot area; multiple marks share one scale so they stay aligned under pan / zoom.

Returns handles
Scale, ColorScale

Functions 6

datumhue.chart.scale.linear

function
datumhue.chart.scale.linear(options: chart.LinearScaleOptions) -> Scale

Construct a linear numeric scale.

Example
-- nice widens the domain to round numbers at both ends.
local grams = datumhue.chart.scale.linear({
    domain = { min = 783, max = 817 },
    nice = true,
})
print(grams.domain.min, grams.domain.max) --> 780.0 820.0

options chart.LinearScaleOptions options 4 keys, 3 inherited

KeyTypeDefaultDescription
follownumberno rolling windowRolling-window size for streaming marks.
From chart.ScaleBase
domaintable | string"auto"{min, max} numeric bounds, or "auto" to fit the data.
nicebooleanfalseExtend the domain to round numbers.
clampbooleanfalseClamp out-of-domain inputs into the range.

In the guide: Chart the answer Query and chart data

datumhue.chart.scale.log

function
datumhue.chart.scale.log(options: chart.LogScaleOptions) -> Scale

Construct a log scale (same numeric-scale fields as linear).

Example
-- 1, 10, 100 and 1000 sit at equal steps along the axis.
local orders = datumhue.chart.scale.log({
    domain = { min = 1, max = 1000 },
    base = 10,
})

options chart.LogScaleOptions options 5 keys, 3 inherited

KeyTypeDefaultDescription
basenumber10Log base; must be positive and not 1.
follownumberno rolling windowRolling-window size for streaming marks.
From chart.ScaleBase
domaintable | string"auto"{min, max} numeric bounds, or "auto" to fit the data.
nicebooleanfalseExtend the domain to round numbers.
clampbooleanfalseClamp out-of-domain inputs into the range.

datumhue.chart.scale.band

function
datumhue.chart.scale.band(options: chart.BandScaleOptions) -> Scale

Construct a categorical (band) scale.

Example
-- One slot per category, in this order; padding is the gap between
-- slots, as a fraction of a slot.
local days = datumhue.chart.scale.band({
    domain = { "Mon", "Tue", "Wed" },
    padding = 0.2,
})
print(#days.categories) --> 3

options chart.BandScaleOptions options 2 keys

KeyTypeDefaultDescription
domain requiredstring[]no defaultNon-empty array of category strings.
paddingnumber0.1Gap between bands, 0..1.

In the guide: Chart the answer

datumhue.chart.scale.time

function
datumhue.chart.scale.time(options: chart.TimeScaleOptions) -> Scale

Construct a time scale. Domain values are epoch-milliseconds.

Example
-- Milliseconds since 1970-01-01 UTC: 2026-10-01 to 2026-10-08.
local week = datumhue.chart.scale.time({
    domain = { min = 1790812800000, max = 1791417600000 },
})
print(week.domain.max - week.domain.min) --> 604800000.0

options chart.TimeScaleOptions options 3 keys, 3 inherited

KeyTypeDefaultDescription
From chart.ScaleBase
domaintable | string"auto"{min, max} numeric bounds, or "auto" to fit the data.
nicebooleanfalseExtend the domain to round numbers.
clampbooleanfalseClamp out-of-domain inputs into the range.

datumhue.chart.scale.color

function
datumhue.chart.scale.color(options: chart.ColorScaleOptions) -> ColorScale

Construct a numeric → color ramp.

Example
-- Exactly one of palette or colors. Past the domain, a value takes
-- the end color.
local heat = datumhue.chart.scale.color({
    palette = "viridis",
    domain = { min = 0, max = 100 },
})
print(heat:map(100) == heat:map(250)) --> true

options chart.ColorScaleOptions options 4 keys

KeyTypeDefaultDescription
colorsColor[]the palette rampArray of at least two color stops. Exactly one of colors or palette.
palette"viridis" | "plasma" | "inferno" | "magma" | "turbo" | "diverging"the colors stopsBuilt-in ramp preset. Exactly one of colors or palette.
domaintable | string"auto"{min, max} numeric bounds, or "auto" to fit the data.
clampbooleantrueClamp out-of-domain inputs to the end stops.

datumhue.chart.scale.color_category

function
datumhue.chart.scale.color_category(options: chart.ColorCategoryOptions) -> ColorScale

Construct a discrete category → color map.

Example
local color = datumhue.color
local ovens = datumhue.chart.scale.color_category({
    categories = { "North", "South" },
    colors = { color("#7fbbb3"), color("#e69875") },
})
print(ovens:map("South") == color("#e69875")) --> true
-- A name not listed takes the next color, cycling past the end.
print(ovens:map("East") == color("#7fbbb3")) --> true

options chart.ColorCategoryOptions options 2 keys

KeyTypeDefaultDescription
categoriesstring[]no listed categoriesCategory names in color order. Unlisted categories register first-seen on lookup.
colorsColor[]the built-in qualitative paletteOne color per category, cycled past the end.

Types 2

chart.Palette

enum
ValueDescription
"viridis"
"plasma"
"inferno"
"magma"
"turbo"
"diverging"

Nested in: chart.ColorScaleOptions

chart.ScaleBase

options

options 3 keys

KeyTypeDefaultDescription
domaintable | string"auto"{min, max} numeric bounds, or "auto" to fit the data.
nicebooleanfalseExtend the domain to round numbers.
clampbooleanfalseClamp out-of-domain inputs into the range.

Extended by: chart.LinearScaleOptions, chart.LogScaleOptions, chart.TimeScaleOptions

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