#92 Create function to derive reference dates in DM domain

[muzzama-1990]

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[github-actions]

Package	Line Rate	Health
sdtm.oak	94%	✔
Summary	94% (1038 / 1105)	✔

[ShiyuC]

@muzzama-1990 Thanks for your great work on these functions! I left some comments for your consideration.

[ShiyuC]

Suggested change

	#' Calculate minimum and maximum date and time in the dataframe
	#' Calculate minimum and maximum date and time in the data frame

[ShiyuC]

Suggested change

	# If both date and time variables are presen use both date and time
	# If both date and time variables are present use both date and time

[muzzama-1990]

updated

[ShiyuC]

I think we need to check if date_variable, time_variable are a string of single character, in case users input a vector of variable names.

[muzzama-1990]

This function is called by the oak_cal_ref_dates and parameters are read from the dataframe hence feel that this assertion is not required.

[muzzama-1990]

@ShiyuC I have addressed your review comments but it looks like the pipelines are failing because of some issue and I see you are working on fixing that in another PR. Once that PR is merged I will rerun the pipelines and the PR will be ready for review.

[ShiyuC]

Looks good to me, thanks Mohsin!