Fix indexing with vector of boolean (#112)

Author: blegat

src/monovec.jl

@@ -39,7 +39,10 @@ end
 # `mutable_copy` recursively copies the vector or vector of integers.
 MA.mutable_copy(m::MV) where {MV<:MonomialVector} = MV(copy(m.vars), MA.mutable_copy(m.Z))
 Base.copy(m::MonomialVector) = MA.mutable_copy(m)
-function Base.getindex(x::MonomialVector, I)
+function Base.getindex(x::MonomialVector, I::AbstractVector{Bool})
+    return typeof(x)(x.vars, x.Z[I])
+end
+function Base.getindex(x::MonomialVector, I::AbstractVector{<:Integer})
     return typeof(x)(x.vars, x.Z[sort(I)])
 end
 Base.getindex(x::MonomialVector, i::Integer) = Monomial(x.vars, x.Z[i])

test/mono.jl

@@ -142,4 +142,13 @@ using Test
             @test y == DynamicPolynomials.MP.mapexponents_to!(z, -, x * y^2, x * y)
         end
     end
+    # TODO add to MP
+    @testset "Indexing with boolean" begin
+        @polyvar x y
+        X = monomials([x, y], 2)
+        @test X[[true, false, true]] == monovec([x^2, y^2])
+        X = monomials([x, y], 0:1)
+        @test filter(mono -> degree(mono) == 1, X) == monovec([x, y])
+        @test filter(mono -> degree(mono) == 0, X) == monovec([x^0])
+    end
 end