improve naming of anonymous functions in aggregate

[bkamins]

October is about to end, so I proposed to solve #1276.

I use standard DataFrame constructor machinery to generate names. The default suffix for lambda function is λ.

Also added makeunique keyword argument as it was missing (as here I guess we should set it to true it by default).

I do not know a better approach to test if a function is anonymous than by checking if first character of its name is # (maybe there is a cleaner solution to this?).

[nalimilan]

Thanks. I guess detecting anonymous functions that way is fine.

I'm not sure using λ for this is a good idea given that it cannot be typed directly at the keyboard. We always provide ASCII variants when using Unicode identifiers, and here there is no ASCII way to access that column. Why not use f instead (or any other ASCII name)?

[nalimilan]

Why df? Sounds like "data frame".

[bkamins]

This is the reason because I want to get a name of f for internal DataFrames.jl purposes. Do you have any suggestion what would be a good name.

I also can change it to an anonymous function call in line 385 if this is preferred.

[nalimilan]

Maybe funname or something like that? Just bikeshedding.

[bkamins]

fixed

[bkamins]

I use λ because:

• this reduces the probability of function name clash;
• it is short (e.g. when printed);
• it produces a valid identifier that can be typed in in any Julia editor and Julia REPL.

If we want ASCII, then maybe lambda would be good (I do not like f because of the name clash possibility)?

[nalimilan]

I'm not a fan of λ/lambda as it's not the most common/explicit term for anonymous functions, especially for people not coming from CS. AFAICT we almost always say "anonymous function" in Julia.

A few ideas: fun, function, agg

[bkamins]

function is OK, as no function will have this name, fun and agg are pretty common when you check students' homework 😄.

[quinnj]

FWIW, I like lambda.

[bkamins]

I merge function version, as it guarantees not to conflict with an actual function name.