Temporal tickFormat for facet reported as invalid if dataset is empty

[mootari]

If a plot defines a temporal tickFormat like %W for a facet, and the dataset is empty, then rendering the Plot will fail with the error:

Error: invalid format: %W

Example:

Plot.barY([], {fy: d => d}).plot({fy: {tickFormat: "%W"}})

For comparison:

Plot.barY([new Date()], {fy: d => d}).plot({fy: {tickFormat: "%W"}})

[Fil]

Same issue with Plot.barY([]).plot({ y: { tickFormat: "%W" } })

Note that there is no possibility to specify that the values are dates by setting the scale’s type ("utc"), since it must be "band".

A work-around for now is to say tickFormat: d3.utcFormat("%W").

[mbostock]

The relevant bit of code is:

plot/src/marks/axis.js

Lines 677 to 678 in 700c6ee

	: typeof tickFormat === "string"
	? (isTemporal(scale.domain()) ? utcFormat : format)(tickFormat)

If the scale domain is empty, I guess we could either ignore the tick format entirely (since it won’t be used to display anything anyway), or we could look at the string and try to guess whether it’s a date format or a number format. Probably the way to do that is to parse it as a number format first, because number formats are stricter than date formats, and only fallback to a date format if the number format fails. But ignoring the tick format if the scale domain is empty seems a lot simpler.

[mbostock]

It’s even more interesting in @Fil’s example because the scale domain isn’t empty per se: it’s defaulting to a linear scale, so the domain is [NaN, NaN] rather than []. Maybe also we should default to an ordinal scale when the domain is empty?

[mbostock]

The error here is expected:

Plot.barY([]).plot({y: {tickFormat: "%W"}})

With barY, the bar starts at 0 and ends at y by default, so we know that the y scale is linear even though there’s no data and hence the %W tick format is invalid. But the equivalent example with barX or setting the x tickFormat shouldn’t error, either.