Module:Weather/sandbox

This is the module sandbox page for Module:Weather (diff).

Module documentation[view] [edit] [history] [purge]

This module can be used to display temperatures in a table. It is under development and is intended to be efficient so a page can hold many tables.

Input numbers must use a hyphen if negative (Unicode minus "−" would give an error).
All displayed numbers (including inputs) use Unicode minus if negative.
The input consists of 13 values, separated by any number of spaces.
Each of the 13 values must be a number. Any invalid value results in the corresponding cell being blank with no error message or tracking category.

The following functions are available:

Function	Input	Output
`CtoF`	°C	°C (°F)
`FfromC`	°C	°F (°C)
`CfromF`	°F	°C (°F)
`FtoC`	°F	°F (°C)

The following templates use the module:

An example using the above templates and the module is at:

sandbox permalink

The output can be examined by entering the following example at Special:ExpandTemplates. The output from each of the following lines is identical.

{{#invoke:weather|CtoF|-10 -5 0 5 10 15 20 25 30 35 40 45 50}}
----
{{#invoke:weather|CfromF|14 23 32 41 50 59 68 77 86 95 104 113 122}}

Optional parameter

|palette=name
Where name is the built-in name of a palette:
cool (default)

cool2 (modified)

cool2avg (modified and intended for average temperatures)

Testing

The function show provides a way to test the color schemes. It generates a graph of how the red, green, and blue portions of the color vary with temperature, and a table of the full range of temperatures in °C.

Optional parameters

Two unnamed parameters may be entered to specify the first and last Celsius temperatures (|-90|59 by default).
The palette can be specified with |palette=name as above.

The following codes produce the same result:

{{#invoke:weather|show}}
{{#invoke:weather|show|palette=cool}}

−90	−89	−88	−87	−86	−85	−84	−83	−82	−81
−80	−79	−78	−77	−76	−75	−74	−73	−72	−71
−70	−69	−68	−67	−66	−65	−64	−63	−62	−61
−60	−59	−58	−57	−56	−55	−54	−53	−52	−51
−50	−49	−48	−47	−46	−45	−44	−43	−42	−41
−40	−39	−38	−37	−36	−35	−34	−33	−32	−31
−30	−29	−28	−27	−26	−25	−24	−23	−22	−21
−20	−19	−18	−17	−16	−15	−14	−13	−12	−11
−10	−9	−8	−7	−6	−5	−4	−3	−2	−1
0	1	2	3	4	5	6	7	8	9
10	11	12	13	14	15	16	17	18	19
20	21	22	23	24	25	26	27	28	29
30	31	32	33	34	35	36	37	38	39
40	41	42	43	44	45	46	47	48	49
50	51	52	53	54	55	56	57	58	59

Modified palette:

{{#invoke:weather|show|palette=cool2}}

−90	−89	−88	−87	−86	−85	−84	−83	−82	−81
−80	−79	−78	−77	−76	−75	−74	−73	−72	−71
−70	−69	−68	−67	−66	−65	−64	−63	−62	−61
−60	−59	−58	−57	−56	−55	−54	−53	−52	−51
−50	−49	−48	−47	−46	−45	−44	−43	−42	−41
−40	−39	−38	−37	−36	−35	−34	−33	−32	−31
−30	−29	−28	−27	−26	−25	−24	−23	−22	−21
−20	−19	−18	−17	−16	−15	−14	−13	−12	−11
−10	−9	−8	−7	−6	−5	−4	−3	−2	−1
0	1	2	3	4	5	6	7	8	9
10	11	12	13	14	15	16	17	18	19
20	21	22	23	24	25	26	27	28	29
30	31	32	33	34	35	36	37	38	39
40	41	42	43	44	45	46	47	48	49
50	51	52	53	54	55	56	57	58	59

This modified palette is intended for average temperatures. It results in good colors between the extreme highest average monthly temperature of +39 °C (102 °F) in Death Valley, California, and −68 °C (−90 °F), the extreme lowest average monthly temperature at Vostok Station, at a high elevation on the Antarctic ice sheet. These are the highest and lowest known average temperatures recorded on Earth, not to be confused with the highest and lowest records, which are quite a bit hotter and colder.

{{#invoke:weather|show|palette=cool2avg}}

−90	−89	−88	−87	−86	−85	−84	−83	−82	−81
−80	−79	−78	−77	−76	−75	−74	−73	−72	−71
−70	−69	−68	−67	−66	−65	−64	−63	−62	−61
−60	−59	−58	−57	−56	−55	−54	−53	−52	−51
−50	−49	−48	−47	−46	−45	−44	−43	−42	−41
−40	−39	−38	−37	−36	−35	−34	−33	−32	−31
−30	−29	−28	−27	−26	−25	−24	−23	−22	−21
−20	−19	−18	−17	−16	−15	−14	−13	−12	−11
−10	−9	−8	−7	−6	−5	−4	−3	−2	−1
0	1	2	3	4	5	6	7	8	9
10	11	12	13	14	15	16	17	18	19
20	21	22	23	24	25	26	27	28	29
30	31	32	33	34	35	36	37	38	39
40	41	42	43	44	45	46	47	48	49
50	51	52	53	54	55	56	57	58	59

The above documentation is transcluded from Module:Weather/sandbox/doc.
Editors can experiment in this module's sandbox and testcases pages.
Subpages of this module.

require('Module:No globals')

local p = {}
local degree = "°" -- used by addUnitNames()
local minus = "−" -- used by makeRow() and makeTable()
local thinSpace = mw.ustring.char(0x2009) -- used by makeCell()

local length, inputUnit, outputUnit, palette, show, cellFormat, precision, decimals

-- Number- and string-handling functions
local function checkForNumber(value)
	return type(tonumber(value)) == "number"
end

local function checkForString(string)
	string = tostring(string)
	if string == "" then
		return nil
	else
		return string
	end
end

-- Error message handling
local message = ""

local function addMessage(newMessage)
	if show then
		if checkForString(message) then
			message = message .. " " .. newMessage
		else
			message = "Notices: " .. newMessage
		end
	end
end

-- Input and output parameters
local function getFormat (frame)
	local inputParameter = frame.args.input
	local outputParameter = frame.args.output
	
	if inputParameter == nil then
		error('Please provide the number of values and a unit in the input parameter')
	else
		-- Find as many as two digits in the input parameter.
		length = tonumber(string.match(inputParameter, "(%d%d?)")) or 13 and addMessage('getFormat has not found a length value in the input parameter; length defaults to "13"')
		-- Find C or F, but not both
		inputUnit = (string.find(inputParameter, "C") and string.find(inputParameter, "F") ) and error("Input unit must be either C (Celsius) or F (Fahrenheit)") or string.match(inputParameter, "([CF])") or error("Please provide an input unit in the input parameter: F for Fahrenheit or C for Celsius", 0)
		-- Make sure nothing except C, F, numbers, or spaces is in the input parameter.
		if string.find(inputParameter, "[^CF%d%s]") then
			addMessage('There are extraneous characters in the <span style="background-color: #EEE; font-family: monospace;">output</span> parameter.')
		end
	end
	
	if outputParameter == nil then
		addMessage('No output format has been provided in the <span style="background-color: #EEE; font-family: monospace;">output</span> parameter, so default values will be used.') -- Since there are default values, the module will still generate output with an empty output parameter.
	else
		cellFormat = {}
		local n = 1
		for unit in outputParameter:gmatch("[CF]") do
			cellFormat[n] = unit
			n = n + 1
			if n > 2 then
				break
			end
		end
		local function setFormat(key, formatVariable, formatValue1, formatValue2)
			if string.find(outputParameter, key) then
				cellFormat[formatVariable] = formatValue1
			else
				cellFormat[formatVariable] = formatValue2
			end
		end
		if cellFormat[1] then
			cellFormat.first = cellFormat[1]
		else
			error('C or F not found in output parameter')
		end
		if cellFormat[2] == nil then
			cellFormat["convertUnits"] = "no"
		else
			if cellFormat[2] == cellFormat[1] then
				error('There should not be two of the same unit name in the output parameter.')
			else
				cellFormat["convertUnits"] = "yes"
			end
		end
		setFormat("unit", "unitNames", "yes", "no")
		setFormat("no ?color", "color", "no", "yes")
		setFormat("sort", "sortable", "yes", "no")
		setFormat("full ?size", "smallFont", "no", "yes")
		setFormat("no ?brackets", "brackets", "no", "yes")
		setFormat("round", "decimals", "0", "")
		if string.find(outputParameter, "line break") then
			cellFormat["lineBreak"] = "yes"
		elseif string.find(outputParameter, "one line") then
			cellFormat["lineBreak"] = "no"
		else
			cellFormat["lineBreak"] = "auto"
		end
		if string.find(outputParameter, "one line") and string.find(outputParameter, "line break") then
			error('Place either "one line" or "line break" in the output parameter, not both')
		end
	end
	if frame.args.palette == nil then
		palette = "cool2avg"
	else
		palette = frame.args.palette
	end
	
	if frame.args.messages == "show" then
		show = true
	else
		show = false
	end
	
	return length, inputUnit, outputUnit, cellFormat, show
end

-- Math functions

local function round(value, decimals)
	value = tonumber(value) or "nil"
	return type(value) == "number" and string.format("%." .. decimals .. "f", value) or addMessage("Format was asked to operate on " .. value .. ", which cannot be converted to a number.", 2) and ""
end

local function convert(value, decimals, unit) -- Unit is the unit being converted from. It defaults to inputUnit.
	if not unit then
		unit = inputUnit
	end
	if checkForNumber(value) then
		local value = tonumber(value)
		if unit == "C" then
			addMessage(value .. " " .. degree .. unit .. " was converted.")
			return round(value * 9/5 + 32, decimals)
		elseif unit == "F" then
			addMessage(value .. " " .. degree .. unit .. " was converted.")
			return round((value - 32) * 5/9, decimals)
		else
			error("Input unit not recognized", 2)
		end
	else
		return "" -- Setting result to empty string if value is not a number avoids concatenation errors.
	end
end

-- Input parsing
local function makeArray(parameter, array, frame)
	getFormat(frame)
	local array = {}
	local n = 1
	for number in parameter:gmatch("%-?%d+%.?%d?") do
		local number = number
		if n == 1 then
			local decimals = number:match("%.(%d+)")
			if decimals == nil then
				precision = "0"
			else
				precision = #decimals
			end
		end
		table.insert(array, n, number)
		n = n + 1
		if n > length then
			break
		end
	end
	if not array[length] then
		addMessage('There are not ' .. length .. ' values in the ' .. parameter .. ' parameter.')
	end
	return array, precision
end

local a, b, c

local function makeArrays(frame)
	getFormat(frame)
	local parameter_a = frame.args.a
	local parameter_b = frame.args.b
	local parameter_c = frame.args.c
	if parameter_a then
		a = makeArray(parameter_a, a, frame)
	else
		error('Please provide a set of numbers in parameter a')
	end
	if parameter_b then
		b = makeArray(parameter_b, b, frame)
	else
		addMessage('There is no content in parameter <span style="background-color: #EEE; font-family: monospace;">b</span>.')
	end
	if parameter_c then
		c = makeArray(parameter_c, c, frame)
	else
		addMessage('There is no content in parameter <span style="background-color: #EEE; font-family: monospace;">c</span>.')
	end
	return a, b, c
end

-- Color generation

local palettes = {
	-- The first three arrays in each palette defines background color using a table of four numbers,
	-- say { 11, 22, 33, 44 } (values in °C).
	-- That means the color is 0 below 11 and above 44, and is 255 from 22 to 33.
	-- The color rises from 0 to 255 between 11 and 22, and falls between 33 and 44.
	cool = {
		{ -42.75,   4.47, 41.5, 60   },
		{ -42.75,   4.47,  4.5, 41.5 },
		{ -90   , -42.78,  4.5, 23   },
		white = { -23.3, 37.8 },
	},
	cool2 = {
		{ -42.75,   4.5 , 41.5, 56   },
		{ -42.75,   4.5 ,  4.5, 41.5 },
		{ -90   , -42.78,  4.5, 23   },
		white = { -23.3, 35 },
	},
	cool2avg = {
		{ -38,   4.5, 25  , 45   },
		{ -38,   4.5,  4.5, 30   },
		{ -70, -38  ,  4.5, 23   },
		white = { -23.3, 25 },
	},
}

local function temperatureColor(palette, value, outRGB)
	--[[ Return style for a table cell based on the given value which
		should be a temperature in °C. ]]
	local backgroundColor, textColor
	value = tonumber(value)
	if value == nil then
		backgroundColor, textColor = 'FFF', '000'
		addMessage('Value supplied to <span style="background-color: #EEE; font-family: monospace;">temperatureColor</span> is not recognized.')
	else
		local min, max = unpack(palette.white or { -23, 35 })
		if value < min or value >= max then
			textColor = 'FFF'
		else
			textColor = '' -- This assumes that black text color is the default for most readers.
		end

		local backgroundRGB = outRGB or {}
		for i, v in ipairs(palette) do
			local a, b, c, d = unpack(v)
			if value <= a then
				backgroundRGB[i] = 0
			elseif value < b then
				backgroundRGB[i] = (value - a) * 255 / (b - a)
			elseif value <= c then
				backgroundRGB[i] = 255
			elseif value < d then
				backgroundRGB[i] = 255 - ( (value - c) * 255 / (d - c) )
			else
				backgroundRGB[i] = 0
			end
		end
		backgroundColor = string.format('%02X%02X%02X', backgroundRGB[1], backgroundRGB[2], backgroundRGB[3])
	end
	if textColor == "" then
		return backgroundColor
	else
		return backgroundColor, textColor
	end
end

local function colorCSS(backgroundColor, textColor)
	if backgroundColor and textColor then
		return 'background: #' .. backgroundColor .. '; color: #' .. textColor .. ';'
	elseif backgroundColor then
		return 'background: #' .. backgroundColor .. ';'
	else
		return ''
	end
end

local function temperatureColorCSS(palette, value, outRGB)
	return colorCSS(temperatureColor(palette, value, outRGB))
end

local function temperatureCSS(value, unit, palette)
	local palette = palettes[palette] or palettes.cool
	local value = tonumber(value)
	if value == nil then
		error('The function <span style="background-color: #EEE; font-family: monospace;">temperatureCSS</span> is receiving a nil value')
	else
		if unit == 'C' then
			return colorCSS(temperatureColor(palette, value))
		elseif unit == 'F' then
			return colorCSS(temperatureColor(palette, convert(value, decimals, 'F')))
		else
			unitError(unit or "nil")
		end
	end
end

local function styleAttribute(palette, value, outRGB)
	local fontSize = "font-size: 85%;"
	local color = temperatureColorCSS(palette, value, outRGB)
	return 'style=\"' .. color .. ' ' .. fontSize .. '\"'
end

local style_attribute = styleAttribute

function p.temperatureStyle(frame) -- used by Template:Average temperature table/color
	local palette = palettes[frame.args.palette] or palettes.cool
	local unit = frame.args.unit or 'C'
	local value = tonumber(frame.args[1])
	if unit == 'C' then
		return styleAttribute(palette, value)
	elseif unit == 'F' then
		return styleAttribute(palette, convert(value, 1, 'F'))
	else
		unitError(unit)
	end
end

p.temperature_style = p.temperatureStyle

--[[ ==== Cell, row, table generation ==== ]]
local outputFormats = {
	high_low_average_F =
		{ first = "F",
		convertUnits = "yes",
		unitNames = "no",
		color = "yes",
		smallFont = "yes",
		sortable = "yes",
		decimals = "0",
		brackets = "yes",
		lineBreak = "auto", },
	high_low_average_C =
		{ first = "C",
		convertUnits = "yes",
		unitNames = "no",
		color = "yes",
		smallFont = "yes",
		sortable = "yes",
		decimals = "0",
		brackets = "yes",
		lineBreak = "auto", },
	high_low_F =
		{ first = "F",
		convertUnits = "yes",
		unitNames = "no",
		color = "no",
		smallFont = "yes",
		sortable = "no",
		decimals = "",
		brackets = "yes",
		lineBreak = "auto", },
	high_low_C =
		{ first = "C",
		convertUnits = "yes",
		unitNames = "no",
		color = "no",
		smallFont = "yes",
		sortable = "no",
		decimals = "0",
		brackets = "yes",
		lineBreak = "auto", },
	average_F =
		{ first = "F",
		convertUnits = "yes",
		unitNames = "no",
		color = "yes",
		smallFont = "yes",
		sortable = "no",
		decimals = "0",
		brackets = "yes",
		lineBreak = "auto", },
	average_C =
		{ first = "C",
		convertUnits = "yes",
		unitNames = "no",
		color = "yes",
		smallFont = "yes",
		sortable = "no",
		decimals = "0",
		brackets = "yes",
		lineBreak = "auto", },
	}

local outputFormat

local function addUnitNames(value, yesOrNo, unit)
	if not unit then unit = inputUnit end
	-- Don't add a unit name to an empty string
	value = yesOrNo == "yes" and checkForString(value) and value .. "&nbsp;" .. degree .. unit or value
	return value
end

local function ifYes(parameter, realization1, realization2)
	local result
	if realization1 then
		if realization2 then
			result = parameter == "yes" and { realization1, realization2 } or { "", "" }
		else
			result = parameter == "yes" and realization1 or ""
		end
	else
		result = ""
		addMessage('<span style="background-color: #EEE; font-family: monospace;">ifYes</span> needs at least one realization')
	end
	return result
end

local function makeCell(outputFormat, a, b, c)
	local cell, cellContent = "", ""
	local colorCSS, otherCSS, titleAttribute, sortkey, attributeSeparator, convertedUnitsSeparator = "", "", "", "", "", "", ""
	local styleAttribute, highLowSeparator, brackets, values, convertedUnits = {"", ""}, {"", ""}, {"", ""}, {"", ""}, {"", ""}
	-- Distinguish styleAttribute variable from styleAttribute function above.
	decimals = ( checkForNumber(outputFormat.decimals) and outputFormat.decimals ) or precision
		--[[ Precision is the number of decimals in the first number of the last array.
			This may be a problem for data from Weatherbase,
			which seems to inappropriately remove .0 from numbers that have it. ]]
	
	if checkForNumber(b) and checkForNumber(a) then
		values, highLowSeparator = { round(a, decimals), round(b, decimals) }, { thinSpace .. "/" .. thinSpace, ifYes(outputFormat.convertUnits, thinSpace .. "/" .. thinSpace) }
	elseif checkForNumber(a) then
		values = { round(a, decimals), "" }
	elseif checkForNumber(c) then
		values = { round(c, decimals), "" }
	end
	if outputFormat.first == inputUnit then
		if outputFormat.convertUnits == "yes" then
			convertedUnits = { addUnitNames(convert(values[1], decimals), outputFormat.unitNames, outputUnit), addUnitNames(convert(values[2], decimals), outputFormat.unitNames, outputUnit) }
		end
		values = { addUnitNames(values[1], outputFormat.unitNames), addUnitNames(values[2], outputFormat.unitNames) }
	elseif outputFormat.first == "C" or outputFormat.first == "F" then
		if outputFormat.convertUnits == "yes" then
			convertedUnits = { addUnitNames(values[1]), addUnitNames(values[2], outputFormat.unitNames) }
		end
		values = { addUnitNames(convert(values[1], decimals), outputUnit), addUnitNames(convert(values[2], decimals), outputFormat.unitNames, outputUnit) }
	else
		if outputFormat.first == nil then
			outputFormat.first = "nil"
		end
		addMessage('<span style="background-color: #EEE; font-family: monospace;">' .. outputFormat.first .. '</span>, the value for <span style="background-color: #EEE; font-family: monospace;">first</span> in <span style="background-color: #EEE; font-family: monospace;">outputFormat</span> is not recognized.')
	end
	--[[
		Regarding line breaks:
		If there are two values, there will be at least three characters: 9/1.
		If there is one decimal, numbers will be three to five characters long
		and there will be 3 to 10 characters total even without unit conversion:
			1.1, 116.5/88.0.
		If there are units, that adds three characters per number: 25 °C/20 °C.
		In each of these cases, a line break is needed so that table cells are not too wide;
		even more so when more than one of these things are true.
		]]
	if outputFormat.convertUnits == "yes" then
		brackets = outputFormat.brackets == "yes" and { "(", ")" } or { "", "" }
		if outputFormat.lineBreak == "auto" then
			convertedUnitsSeparator = ( checkForString(values[2]) or decimals ~= "0" or outputFormat.showUnits == "yes" ) and "<br>" or "&nbsp;"
		else
			convertedUnitsSeparator = outputFormat.lineBreak == "yes" and "<br>" or outputFormat.lineBreak == "no" and "&nbsp;" or error('Value for lineBreak not recognized')
		end
	end
	
	cellContent = values[1] .. highLowSeparator[1] .. values[2] .. convertedUnitsSeparator .. brackets[1] .. convertedUnits[1] .. highLowSeparator[2] .. convertedUnits[2] .. brackets[2]
	
	if checkForNumber(c) then
		colorCSS = outputFormat.color == "yes" and temperatureCSS(c, inputUnit, palette) or ""
		if checkForNumber(b) and checkForNumber(a) then
			local attributeValue = outputFormat.first == inputUnit and c or convert(c, decimals)
			sortkey = outputFormat.sortable == "yes" and " data-sort-value=\"" .. attributeValue .. "\"" or ""
			titleAttribute = " title=\"Average temperature: " .. attributeValue .. " " .. degree .. outputFormat.first .. "\""
		end
	elseif checkForNumber(b) then
		colorCSS = ""
	elseif checkForNumber(a) then
		colorCSS = outputFormat.color == "yes" and temperatureCSS(a, inputUnit, palette) or ""
	else
		addMessage('Neither a nor b nor c are strings.')
	end
	otherCSS = outputFormat.smallFont == "yes" and "font-size: 85%;" or ""
	if checkForString(colorCSS) or checkForString(otherCSS) then
		styleAttribute = { "style=\"", "\"" }
	end
	
	if checkForString(otherCSS) or checkForString(colorCSS) or checkForString(titleAttribute) or checkForString(sortkey) then
		attributeSeparator = " | "
	end
	cell = "\n| " .. styleAttribute[1] .. colorCSS .. otherCSS .. styleAttribute[2] .. titleAttribute .. sortkey .. attributeSeparator .. cellContent
	return cell
end

function p.makeRow(frame)
	makeArrays(frame)
	local output = ""
	if frame.args[1] then
		output = "\n|-"
		output = output .. "\n! " .. frame.args[1]
		if frame.args[2] then
			output = output .. " !! " .. frame.args[2]
		end
	end
	if cellFormat then
		outputFormat = cellFormat
	end
	if a and b and c then
		for i = 1, length do
			if not outputFormat then
				outputFormat = outputFormats.high_low_average_F
			end
			output = output .. makeCell(outputFormat, a[i], b[i], c[i])
		end
	elseif a and b then
		for i = 1, length do
			if not outputFormat then
				outputFormat = outputFormats.high_low_F
			end
			output = output .. makeCell(outputFormat, a[i], b[i])
		end
	elseif a then
		for i = 1, length do
			if not outputFormat then
				outputFormat = outputFormats.average_F
			end
			output = output .. makeCell(outputFormat, a[i])
		end
	end
	output = mw.ustring.gsub(output, "([%p%s])-(%d)", "%1" .. minus .. "%2")
	return output
end

function p.makeTable(frame)
	makeArrays(frame)
	local output = "{| class=\"wikitable center nowrap\""
	if cellFormat then
		outputFormat = cellFormat
	end
	if a and b and c then
		for i = 1, length do
			if not outputFormat then
				outputFormat = outputFormats.high_low_average_F
			end
			output = output .. makeCell(outputFormat, a[i], b[i], c[i])
		end
	elseif a and b then
		for i = 1, length do
			if not outputFormat then
				outputFormat = outputFormats.high_low_F
			end
			output = output .. makeCell(outputFormat, a[i], b[i])
		end
	elseif a then
		for i = 1, length do
			if not outputFormat then
				outputFormat = outputFormats.average_F
			end
			output = output .. makeCell(outputFormat, a[i])
		end
	end
	output = mw.ustring.gsub(output, "([%p%s])-(%d)", "%1" .. minus .. "%2")
		--[[  Replaces hyphens that have a punctuation or space character before them and a number after them,
				making sure that hyphens in "data-sort-type" are not replaced with minuses.
				If Lua had (?<=), a capture would not be necessary.  ]]
	output = output .. "\n|}"
	if show then
		output = output .. "\n\n<span style=\"color: red; font-size: 80%; line-height: 100%;\">" .. message .. "</span>"
	end
	return output
end



local chart = [[
{{Graph:Chart
|width=600
|height=180
|xAxisTitle=Celsius
|yAxisTitle=__COLOR
|type=line
|x=__XVALUES
|y=__YVALUES
|colors=__COLOR
}}
]]

function p.show(frame)
	-- For testing, return wikitext to show graphs of how the red/green/blue colors
	-- vary with temperature, and a table of the resulting colors.
	local function collection()
		-- Return a table to hold items.
		return {
			n = 0,
			add = function (self, item)
				self.n = self.n + 1
				self[self.n] = item
			end,
			join = function (self, sep)
				return table.concat(self, sep)
			end,
		}
	end
	local function make_chart(result, color, xvalues, yvalues)
		result:add('\n')
		result:add(frame:preprocess((chart:gsub('__[A-Z]+', {
			__COLOR = color,
			__XVALUES = xvalues:join(','),
			__YVALUES = yvalues:join(','),
		}))))
	end
	local function with_minus(value)
		if value < 0 then
			return minus .. tostring(-value)
		end
		return tostring(value)
	end
	local args = frame.args
	local first = args[1] or -90
	local last = args[2] or 59
	local palette = palettes[args.palette] or palettes.cool
	local xvals, reds, greens, blues = collection(), collection(), collection(), collection()
	local wikitext = collection()
	wikitext:add('{| class="wikitable"\n|-\n')
	local columns = 0
	for celsius = first, last do
		local backgroundRGB = {}
		local style = styleAttribute(palette, celsius, backgroundRGB)
		local R = math.floor(backgroundRGB[1])
		local G = math.floor(backgroundRGB[2])
		local B = math.floor(backgroundRGB[3])
		xvals:add(celsius)
		reds:add(R)
		greens:add(G)
		blues:add(B)
		wikitext:add('| ' .. style .. ' | ' .. with_minus(celsius) .. '\n')
		columns = columns + 1
		if columns >= 10 then
			columns = 0
			wikitext:add('|-\n')
		end
	end
	wikitext:add('|}\n')
	make_chart(wikitext, 'Red', xvals, reds)
	make_chart(wikitext, 'Green', xvals, greens)
	make_chart(wikitext, 'Blue', xvals, blues)
	return wikitext:join()
end

return p, palettes