# JuliaLang/julia

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 # This file is a part of Julia. License is MIT: http://julialang.org/license module Order ## notions of element ordering ## export # not exported by Base Ordering, Forward, Reverse, Lexicographic, By, Lt, Perm, ReverseOrdering, ForwardOrdering, LexicographicOrdering, DirectOrdering, lt, ord, ordtype abstract Ordering immutable ForwardOrdering <: Ordering end immutable ReverseOrdering{Fwd<:Ordering} <: Ordering fwd::Fwd end ReverseOrdering(rev::ReverseOrdering) = rev.fwd ReverseOrdering{Fwd}(fwd::Fwd) = ReverseOrdering{Fwd}(fwd) typealias DirectOrdering Union{ForwardOrdering,ReverseOrdering{ForwardOrdering}} const Forward = ForwardOrdering() const Reverse = ReverseOrdering(Forward) immutable LexicographicOrdering <: Ordering end const Lexicographic = LexicographicOrdering() immutable By{T} <: Ordering by::T end immutable Lt{T} <: Ordering lt::T end immutable Perm{O<:Ordering,V<:AbstractVector} <: Ordering order::O data::V end lt(o::ForwardOrdering, a, b) = isless(a,b) lt(o::ReverseOrdering, a, b) = lt(o.fwd,b,a) lt(o::By, a, b) = isless(o.by(a),o.by(b)) lt(o::Lt, a, b) = o.lt(a,b) lt(o::LexicographicOrdering, a, b) = lexcmp(a,b) < 0 function lt(p::Perm, a::Integer, b::Integer) da = p.data[a] db = p.data[b] lt(p.order, da, db) | (!lt(p.order, db, da) & (a < b)) end function lt(p::Perm{LexicographicOrdering}, a::Integer, b::Integer) c = lexcmp(p.data[a], p.data[b]) c != 0 ? c < 0 : a < b end ordtype(o::ReverseOrdering, vs::AbstractArray) = ordtype(o.fwd, vs) ordtype(o::Perm, vs::AbstractArray) = ordtype(o.order, o.data) # TODO: here, we really want the return type of o.by, without calling it ordtype(o::By, vs::AbstractArray) = try typeof(o.by(vs[1])) catch; Any end ordtype(o::Ordering, vs::AbstractArray) = eltype(vs) function ord(lt, by, rev::Bool, order::Ordering=Forward) o = (lt===isless) & (by===identity) ? order : (lt===isless) & (by!==identity) ? By(by) : (lt!==isless) & (by===identity) ? Lt(lt) : Lt((x,y)->lt(by(x),by(y))) rev ? ReverseOrdering(o) : o end end