Middle(x,y) for DateTime, Char, and others

Internals & Design
1

Should these methods exist?

  middle(x, y)


  Compute the middle of two numbers x and y, which is equivalent in both value and
  type to computing their mean ((x + y) / 2).

julia> middle(now(), now())
ERROR: MethodError: no method matching middle(::DateTime, ::DateTime)

julia> middle('a','c')
ERROR: MethodError: no method matching middle(::Char, ::Char)
  • Char seems likely.
  • For DateTime, which has 1 ms precision, I’m not sure what the rounding rules are.
  • For Date, which has 1 day precision, likewise.
  • Are there other types that should have these methods?
2

What would middle('a','b') return?

Considering that this function is in the Statistics module, I’m not sure it makes sense to define it for non-numeric types like Char.

3

I don’t see that statistics applies only to numbers. Affine quantities like Dates and Fahrenheits can theoretically all compute midpoints by something like (though not exactly)

middle(x,y) = (x - y) / 2 + y

instead of

(x + y) / 2

I propose it would give an InexactError, as would middle(today, tomorrow).

On the other hand, middle(yesterday, tomorrow) == today and middle(32.0°F, 33.0°F) == 32.5°F where currently it fails on division.

4

For reference, see middle is undefined for Date and DateTime (so median does not work) · Issue #47 · JuliaStats/Statistics.jl · GitHub.