Proposal: make first and last always return 1 element, let take return from end of list

[rgwood]

Following some discussion on Discord and in this issue, I would like to propose the following changes:

1. Remove the rows parameter from first and last so they always return a single item
   1. Makes the commands' return type consistent
   2. Brings Nu's behaviour in line with many other languages
2. Add negative number support to take so take -3 returns the last 3 elements.
   1. Inspired by Python's negative indexing (and has been suggested a few times by Python users)
   2. Lets us support existing last n functionality without adding a new command

Examples

[0 1 2] | first 2 # will no longer work
[0 1 2] | take 2  # will need to do this instead

[0 1 2] | last 2  # will no longer work
[0 1 2] | take -2 # will need to do this instead

Language Comparison

Functionality	First element	n-th element	Last element	First n elements	Last n elements
Return Type	T	T	T	List<T>	List<T>
Python (more_)itertools	first	nth	last	take(n)	arr[-n:], tail(n)
Javascript (lodash)	head()	nth	last()	take(n)	takeRight(n)
.NET / C# / LINQ	First()	ElementAt()	Last()	Take(n)	TakeLast(n), array[^n..]
Rust	first()	nth()	last()	take(n)	v[v.len()-3..]?
Scala	head	drop(n-1).next	last	take(n)	.takeRight(n)
Nushell (current)	first	get n	last	first n, take n	last n
Nushell (proposed)	first	get n	last	take n	take -n

Next Steps

If this isn't too controversial I can implement it soon.

Additional context and details

No response

[theAkito]

Three more for the fun of it.

Functionality	First element	n-th element	Last element	First n elements	Last n elements
Kotlin	first()	[n] or get(n)	last()	take(n)	takeLast(n)
Nim	[0]	[n]	[^1] or pop	[0..n]	[^n..^1]
Borg	N/A	N/A	N/A	--first n	--last n

Lets us support existing last n functionality without adding a new command

If this is guaranteed, all is fine.

[dandavison]

LGTM!

[raccmonteiro]

this does not look very complex for someone new to rust. I would like to try

[rgwood]

@raccmonteiro Thanks for the offer!

I'm planning on doing this one because it will require a small rewrite of last; to make a long story short last doesn't check types properly and I want to clean that up while I'm in the area.

[raccmonteiro]

yeah no problem :) I will find another issue