automatically imputing time units for ordinal scales

[kanitw]

(Forked from #6589)

For example, there are 7 days in a week, but without manual imputation we show this:

cc: @willium

[kanitw]

Though it's unclear (1) what should be the syntax to enable / disable automatic imputation and (2) which time units should be automatically imputed.

For (2), quarter, month, day obviously should be imputed. But what about "date", "hours", "seconds"?

[willium]

(1) If we make tick counts better for the day time units (as in the second screenshot in the original issue), will it be necessary to impute?

for (2) I think those ought to be as well (+ minutes) so long as we don't allow for fractional dates, hours, or minutes, seconds.

[willium]

For documentation's sake, I believe Vega's timeSequence expression will be useful for doing the imputation.

[willium]

For (1) could we not use the existing nice property? for example

If not, I propose we add a boolean temporal scale property impute much like how continuous scales have a interpolate property.

[domoritz]

Help me remember, but I think we removed imputation from time units with ordinal some time ago since we don’t really want imputation for any time unit (e.g. month date) with too many values. While I agree that imputation is often useful, I don’t think I want it to be the default.

[colleen-love]

Would it be possible to update the documentation to say that it's not possible to impute temporal series? Or log a warning in the console?