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Add isdisjoint #34427

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merged 1 commit into from
Jan 20, 2020
Merged

Add isdisjoint #34427

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28 changes: 27 additions & 1 deletion base/abstractset.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -260,6 +260,8 @@ true
"""
issubset, ⊆, ⊇

const FASTIN_SET_THRESHOLD = 70

function issubset(l, r)
if haslength(r) && (isa(l, AbstractSet) || !hasfastin(r))
rlen = length(r) # conditions above make this length computed only when needed
Expand All @@ -269,7 +271,7 @@ function issubset(l, r)
end
# when `in` would be too slow and r is big enough, convert it to a Set
# this threshold was empirically determined (cf. #26198)
if !hasfastin(r) && rlen > 70
if !hasfastin(r) && rlen > FASTIN_SET_THRESHOLD
return issubset(l, Set(r))
end
end
Expand Down Expand Up @@ -375,6 +377,30 @@ function issetequal(l, r)
return issetequal(Set(l), Set(r))
end

## set disjoint comparison
"""
isdisjoint(v1, v2) -> Bool

Returns whether the collections `v1` and `v2` are disjoint, i.e. whether
their intersection is empty.

!!! compat "Julia 1.5"
This function requires at least Julia 1.5.
"""
function isdisjoint(l, r)
function _isdisjoint(l, r)
hasfastin(r) && return !any(in(r), l)
hasfastin(l) && return !any(in(l), r)
haslength(r) && length(r) < FASTIN_SET_THRESHOLD &&
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Just a note, in issubset the conversion to Set can be done only if haslength(r), here you made the opposite choice... Was it for a specific reason? (I didn't think much about it, but indeed converting to Set when length is unknown seems like a better choice to me; what about updating issubset then?).

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Yes, converting to Set in general seemed like a good idea to me, with the exception of a fast path when the thing we're iterating over happens to be short.

return !any(in(r), l)
return !any(in(Set(r)), l)
end
if haslength(l) && haslength(r) && length(r) < length(l)
return _isdisjoint(r, l)
end
_isdisjoint(l, r)
end

## partial ordering of sets by containment

==(l::AbstractSet, r::AbstractSet) = length(l) == length(r) && l ⊆ r
Expand Down
1 change: 1 addition & 0 deletions base/exports.jl
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Expand Up @@ -502,6 +502,7 @@ export
in,
intersect!,
intersect,
isdisjoint,
isempty,
issubset,
issetequal,
Expand Down
6 changes: 5 additions & 1 deletion test/sets.jl
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Expand Up @@ -301,13 +301,15 @@ end
@test !(Set([1,2,3]) <= Set([1,2,4]))
end

@testset "issubset, symdiff" begin
@testset "issubset, symdiff, isdisjoint" begin
for S in (Set, BitSet, Vector)
for (l,r) in ((S([1,2]), S([3,4])),
(S([5,6,7,8]), S([7,8,9])),
(S([1,2]), S([3,4])),
(S([5,6,7,8]), S([7,8,9])),
(S([1,2,3]), S()),
(S(), S()),
(S(), S([1,2,3])),
(S([1,2,3]), S([1])),
(S([1,2,3]), S([1,2])),
(S([1,2,3]), S([1,2,3])),
Expand All @@ -317,6 +319,8 @@ end
@test issubset(intersect(l,r), r)
@test issubset(l, union(l,r))
@test issubset(r, union(l,r))
@test isdisjoint(l,l) == isempty(l)
@test isdisjoint(l,r) == isempty(intersect(l,r))
if S === Vector
@test sort(union(intersect(l,r),symdiff(l,r))) == sort(union(l,r))
else
Expand Down