add keepat! and insert! and pushfirst!

[bkamins]

In the future consider adding keepat! support (introduced in Julia 1.7).

[Chandu-4444]

Can I try adding insert!? Can you tell me how and where to start writing this function?

[bkamins]

I think insert! is hard to start with (unless you are really experienced with Julia).

You would need to use:

• https://github.com/JuliaData/DataFrames.jl/blob/main/src/dataframe/dataframe.jl#L1416
• https://github.com/JuliaData/DataFrames.jl/blob/main/src/dataframe/dataframe.jl#L1666
• https://github.com/JuliaData/DataFrames.jl/blob/main/src/dataframerow/dataframerow.jl#L501

and define similar insert! three methods for insert!. I encourage to review this source code and decide, but you will see that it is not an easy code and insert! will be a bit more complex than push! (not much but a still).

keepat! should be much easier as you just need to call deleteat! with an inverse selector (at least in the easiest scenario, i.e. not pushing performance to the limits). The only thing to be careful about is that keepat! will either need to be imported from Base or defined internally and exported depending on Julia version the user is on.

[bkamins]

If you are looking for easy PRs I would recommend:

• add view::Bool kwarg to first and last #2845
• Add reverse and reverse! functions similar to sort and sort! #2438
• Allow keeping first or last observation with unique function  #2443 (this one is a bit harder)

[bkamins]

Also to complete the list of possible additions:

• resize!
• pop!
• popat!
• popfirst!
• keepat!
• insert!
• pushfirst!
• prepend!