Test and document copy(xf, eachrow(df))

src/processes.jl

@@ -634,6 +634,18 @@ julia> using StructArrays
 
 julia> @assert copy(Map(x -> (a=x, b=x^2)), StructVector, 1:1) == StructVector(a=[1], b=[1])
 ```
+
+As `DataFrame` does not have iteration interface yet, use `eachrow` to
+process rows of a dataframe.  Note that `copy` automatically use
+`DataFrame` as default output type in this case:
+
+```jldoctest; setup = :(using Transducers)
+julia> using DataFrames
+
+julia> @assert copy(
+           Map(x -> (A = x.a + 1, B = x.b + 1)),
+           eachrow(DataFrame(a = [1], b = [2])),
+       ) == DataFrame(A = [2], B = [3])
 """
 Base.copy(xf::Transducer, ::Type{T}, foldable) where {T} = append!!(xf, Empty(T), foldable)
 Base.copy(xf::Transducer, foldable) = copy(xf, _materializer(foldable), foldable)

test/Project.toml

@@ -3,6 +3,7 @@ Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 ArgCheck = "dce04be8-c92d-5529-be00-80e4d2c0e197"
 BangBang = "198e06fe-97b7-11e9-32a5-e1d131e6ad66"
 BlockArrays = "8e7c35d0-a365-5155-bbbb-fb81a777f24e"
+Compat = "34da2185-b29b-5c13-b0c7-acf172513d20"
 DataFrames = "a93c6f00-e57d-5684-b7b6-d8193f3e46c0"
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 Distributed = "8ba89e20-285c-5b6f-9357-94700520ee1b"

test/preamble.jl

@@ -1,3 +1,4 @@
+using Compat: eachrow
 using Test
 using Random
 using SparseArrays: issparse, sparse

test/test_copy.jl

@@ -22,8 +22,7 @@ end
     end
     @testset "$copy(_, eachrow(df))" begin
         df = DataFrame(a=[1], b=[2])
-        @test_broken copy(Map(identity), eachrow(df)) ==ₜ df
-        # requires https://github.com/JuliaData/DataFrames.jl/pull/2055
+        @test copy(Map(identity), eachrow(df)) ==ₜ df
     end
 end