Add most functions to the Expr class so that they're chainable.

[deanm0000]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Instead of doing

df.select(
    F.abs(
        col("id1")
        )
    .alias("id1")
    )

It would be nicer to do

df.select(
    col("id1")
    .abs()
    .alias("id1")
    )

Describe the solution you'd like
This is already partly there, for example, alias is already in the Expr class. It would be a bit tedious but easy to add under class Expr, for example:

def abs(self) -> datafusion.Expr:
    """Return the absolute value of a given number.

    Returns:
    --------
    Expr
        A new expression representing the absolute value of the input expression.
    """
    return F.abs(self)

Describe alternatives you've considered
if it weren't for the type hinter, monkey patching.

Additional context
There will still be functions that don't make sense to chain off of a call to col such as when since it doesn't return an Expr. But, even functions that take multiple inputs can have this for instance col("a").atan2("b"). Additionally, this is completely backwards compatible since I'm not proposing eliminating the functions module.

[deanm0000]

Is this something a PR would be accepted for or no?

[timsaucer]

This sounds like a great idea!

I don’t think we want it for every function, but definitely many of them - probably a majority.

Things like regr_count probably don’t benefit from this but abs absolutely does (pun intended).

Thank you for filing the issue!

[deanm0000]

@timsaucer I put in a draft PR that does all the one input arg functions.

Is your reluctance to putting every function in due to clutter or that more funcs is (seemingly) more work? For the draft, I wrote a script to generate the funcs so filtering some out is actually more work. That said, I didn't type each of them manually so don't feel bad in chopping some of them.

As to the general point of clutter, I made a comment in the PR advocating the idea of categorizing functions and putting them in namespaces.

[timsaucer]

The reluctance is only because some of them I think doesn't improve ergonomics for our users. The 1 and 2 argument functions are absolutely helpful. But I can be persuaded otherwise.

[ion-elgreco]

Actually a duplicate of #876