Initial offset design ideas

[AdRiley]

Pull Request Description

Column.Offset takes a number n and a mode of what to do with the missing values.

Defaults to n of -1 and ..Nothing for the missing values

Can also use closest value

Or wrap the values around

Or enter a constant value

This can then be used in an expression

Table.Offset

Questions:

• Do we copy the columns or offset on top of the existing columns? (I think copy to allow easier month by month comparisons for example)
• If we copy what are the names of the new columns?
• Do we offer the ability to customise the new names?

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[radeusgd]

• Do we offer the ability to customise the new names?

What if Table.offset only allows one input column, not many? Then it could have an optional argument new_name, working much like in Table.set.

Or do we expect to be setting offsets of many columns at once often? If yes, perhaps we could have something like name_suffix?

[jdunkerley]

Column design looks great - Closest_Value meanss Previous if negative, Next if positive.

We could have set mode for it:

• Add (default): offset([xx],shift) as new name
• Update - replace existing column

I would keep the customization on names to use rename_columns.

We should let it work on multiple columns at once as that is useful.