fix: clean up grammar to align with each plot requirement

[jooyoungseo]

BarData

It looks like BarData is defined to be allowed to take either number or string array for x. However, bar plot needs to take a categorical variable only for x axis and numeric variable for y (of course, the flipped bar plot is the other way around):

https://github.com/xability/maidr-ts/blob/c0c42b2177192679b4d7d07ed86d84c4478651ba/src/plot/grammar.ts#L14-L22

Shouldn't we restrict the type of x to be string array only for bar plot?

LineData

Although numeric variable is possible for x variable, date variable is a typical use case for x axis in line plot. Shouldn't we allow date variable for x axis in line plot? I know, date is a subtype of number, but it would be more intuitive to allow date variable for x axis in line plot for better manipulation.

https://github.com/xability/maidr-ts/blob/c0c42b2177192679b4d7d07ed86d84c4478651ba/src/plot/grammar.ts#L24-L30

[saaivenk]

Professor @jooyoungseo , since we are having our own unique functionalities, it would be better to represent the data for our need than having them for data visualization standards. Could we please close this ticket?

[jooyoungseo]

@SaaiVenkat Let's discuss further on the grammar and refactor if needed later.