xunker / array-subindex Goto Github PK

Array indexes can be ranges, or can be integers passed with a length.

Right now the gem handles these in the same way that the base Array class does:

[1,2,3][0..1]
# => [1,2]

[1,2,3][1,2]
# => [2,3]

That's all well and good, but they should do something... better. But what?

Ruby (2.0.0 at least) supports Ranges with Float boundaries. I'd like to see this:

[1,2,3,4][0.5..2.5]
# => [1.5, 2.5, 3.5]

%w[foo bar baz qux][0.5..2.5]
# => ["oob", "arb", "azq"]

That's easy. That's approach would also work verbatin with a length argument with the array index. But what about irregular ranges like [0.5..10.9]? What would the stepping be?

I noticed the following in the docs:

[1,2,3][0.25] == 1.75
#1/4 of index 0 + 3/4 of index 1

I would have expected the output values to be more continuous, and to follow the following pattern:

[1,2,3][0.25] == 1.25
#3/4 of index 0 + 1/4 of index 1

That is to say, the limit of #[] as the index approaches n from above where n is an integer should be #[n], not #[n+1]. Similarly, the limit of #[] as the index approaches n from below should be #[n], not #[n-1].

Similarly, I would not have expected the following:

[1,2,3][1.001] == 2.999

I would have instead expected:

[1,2,3][1.001] = 2.001

Now it's TLDR time!

I think it's fair to say that linear interpolation is a reasonable assumption. I wouldn't necessarily expect it to figure out the following:

[1,4,9][1.5] = 6.25

Especially since fitting functions always makes assumptions, and while it is easy for us to assume the following is an exponential function, one could also make the case that it's just a funky 3rd order polynomial and get a different answer.

[1,2,4,8][1.5] = 2.8284

[1] pry(main)> require 'array/subindex'
NoMethodError: undefined method to_f' for 0..-1:Range from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/array-subindex-1.2.0/lib/array/subindex.rb:5:in[]'
[2] pry(main)>
NoMethodError: undefined method to_f' for 0..-1:Range from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/array-subindex-1.2.0/lib/array/subindex.rb:5:in[]'
[2] pry(main)> puts 2
NoMethodError: undefined method to_f' for 0..-1:Range from C:/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/array-subindex-1.2.0/lib/array/subindex.rb:5:in[]'

Everything I press it shows this error. IRB/ruby(as ruby file.rb) works fine.

We can do endless ranges in Ruby < 2.6 with (0..Float::INFINITY), and in Ruby >= 2.6 with (0..) or (0..nil).

Also, in Ruby 2.7 we now have beginless ranges: [..100]

These may already work, because they can be worked with as an array, but we need to add tests for that.