allow scalar broadcasting into an empty data frame

docs/src/lib/indexing.md

@@ -172,9 +172,10 @@ In such an operation `AbstractDataFrame` is considered as two-dimensional and `D
     `DataFrameRow` is considered to be column-oriented.
 
 Additional rules:
-* in the `df[CartesianIndex(row, col)] .= v`, `df[row, col] .= v` and `df[row, cols] .= v` syntaxes the assignment to `df` is performed in-place;
+* in the `df[CartesianIndex(row, col)] .= v`, `df[row, col] .= v` syntaxes we broadcast `v` into the contents of `df[row, col]` (this is consistent with Base behavior);
+* in the `df[row, cols] .= v` syntaxes the assignment to `df` is performed in-place;
 * in the `df[rows, col] .= v` and `df[rows, cols] .= v` syntaxes the assignment to `df` is performed in-place;
-* in the `df[!, col] .= v` syntax column `col` is replaced by a freshly allocated vector; if `col` is `Symbol` and it is missing from `df` then a new column is added;
+* in the `df[!, col] .= v` syntax column `col` is replaced by a freshly allocated vector; if `col` is `Symbol` and it is missing from `df` then a new column is added; the length of the column is always the value of `nrow(df)` before the assignment takes place;
 * `df[!, cols] = v` syntax is currently disallowed, but is planned to be supported in the future;
 * `df.col .= v` syntax is allowed and performs in-place assignment to an existing vector `df.col`.
 * in the `sdf[CartesianIndex(row, col)] .= v`, `sdf[row, col] .= v` and `sdf[row, cols] .= v` syntaxes the assignment to `sdf` is performed in-place;

src/other/broadcasting.jl

@@ -78,7 +78,8 @@ struct LazyNewColDataFrame{T}
     col::T
 end
 
-# we allow LazyNewColDataFrame only for data frames with at least one column
+# we allow LazyNewColDataFrame also for data frames
+# that are empty, ie. `nrow(df) == 0`; in this case we create a 0 length column
 Base.axes(x::LazyNewColDataFrame) = (Base.OneTo(nrow(x.df)),)
 
 # ColReplaceDataFrame is reserved for future extensions if we decide to allow df[!, cols] .= v
@@ -90,15 +91,16 @@ Base.axes(x::LazyNewColDataFrame) = (Base.OneTo(nrow(x.df)),)
 
 # Base.axes(x::ColReplaceDataFrame) = axes(x.df)
 
-Base.maybeview(df::AbstractDataFrame, idx::CartesianIndex{2}) = view(df, idx[1], idx[2])
+Base.maybeview(df::AbstractDataFrame, idx::CartesianIndex{2}) = df[idx]
+Base.maybeview(df::AbstractDataFrame, row::Integer, col::ColumnIndex) = df[row, col]
 Base.maybeview(df::AbstractDataFrame, rows, cols) = view(df, rows, cols)
 
 function Base.maybeview(df::DataFrame, ::typeof(!), cols)
     if !(cols isa ColumnIndex)
         throw(ArgumentError("broadcasting with column replacement is currently allowed only for single column index"))
     end
-    if ncol(df) == 0
-        throw(ArgumentError("broadcasting into a data frame with no columns is not allowed"))
+    if !(cols isa Symbol) && cols > ncol(df)
+        throw(ArgumentError("creating new columns using an integer index by broadcasting is disallowed"))
     end
     # in the future we might allow cols to target multiple columns
     # in which case ColReplaceDataFrame(df, index(df)[cols]) will be returned
@@ -108,14 +110,11 @@ end
 Base.maybeview(df::SubDataFrame, ::typeof(!), idxs) =
     throw(ArgumentError("broadcasting with ! row selector is not allowed for SubDataFrame"))
 
-function Base.copyto!(lazydf::LazyNewColDataFrame, bc::Base.Broadcast.Broadcasted)
-    if isempty(lazydf.df)
-        throw(ArgumentError("creating a column via broadcasting is not allowed on empty data frames"))
-    end
-    if bc isa Base.Broadcast.Broadcasted{<:Base.Broadcast.AbstractArrayStyle{0}} &&
-       bc.f === identity && bc.args isa Tuple{Any} && Base.Broadcast.isflat(bc)
-        T = typeof(bc.args[1][])
-        col = similar(Vector{T}, nrow(lazydf.df))
+function Base.copyto!(lazydf::LazyNewColDataFrame, bc::Base.Broadcast.Broadcasted{T}) where T
+    if bc isa Base.Broadcast.Broadcasted{<:Base.Broadcast.AbstractArrayStyle{0}}
+        bc_tmp = Base.Broadcast.Broadcasted{T}(bc.f, bc.args, ())
+        v = Base.Broadcast.materialize(bc_tmp)
+        col = similar(Vector{typeof(v)}, nrow(lazydf.df))
         copyto!(col, bc)
     else
         col = Base.Broadcast.materialize(bc)

test/broadcasting.jl

@@ -598,14 +598,67 @@ end
     @test_throws BoundsError dfr[10] .= ones(3)
     @test_throws ArgumentError dfr[:z] .= ones(3)
     @test df == cdf
+
+    df = DataFrame()
+    @test_throws DimensionMismatch df[!, :a] .= sin.(1:3)
+    df[!, :b] .= sin.(1)
+    df[!, :c] .= sin(1) .+ 1
+    @test df == DataFrame(b=Float64[], c=Float64[])
 end
 
 @testset "empty data frame corner case" begin
     df = DataFrame()
     @test_throws ArgumentError df[!, 1] .= 1
-    @test_throws ArgumentError df[!, :a] .= [1]
-    @test_throws ArgumentError df[!, [:a,:b]] .= [1]
-    @test df == DataFrame()
+    @test_throws ArgumentError df[!, 2] .= 1
+    @test_throws ArgumentError df[!, [:a, :b]] .= [1]
+    @test_throws ArgumentError df[!, [:a, :b]] .= 1
+    @test_throws DimensionMismatch df[!, :a] .= [1 2]
+    @test_throws DimensionMismatch df[!, :a] .= [1, 2]
+    @test_throws DimensionMismatch df[!, :a] .= sin.(1) .+ [1, 2]
+
+    for rhs in [1, [1], Int[], "abc", ["abc"]]
+        df = DataFrame()
+        df[!, :a] .= rhs
+        @test size(df) == (0, 1)
+        @test eltype(df[!, 1]) == (rhs isa AbstractVector ? eltype(rhs) : typeof(rhs))
+
+        df = DataFrame()
+        df[!, :a] .= length.(rhs)
+        @test size(df) == (0, 1)
+        @test eltype(df[!, 1]) == Int
+
+        df = DataFrame()
+        df[!, :a] .= length.(rhs) .+ 1
+        @test size(df) == (0, 1)
+        @test eltype(df[!, 1]) == Int
+
+        df = DataFrame()
+        @. df[!, :a] = length(rhs) + 1
+        @test size(df) == (0, 1)
+        @test eltype(df[!, 1]) == Int
+
+        df = DataFrame(x=Int[])
+        df[!, :a] .= rhs
+        @test size(df) == (0, 2)
+        @test eltype(df[!, 2]) == (rhs isa AbstractVector ? eltype(rhs) : typeof(rhs))
+
+        df = DataFrame(x=Int[])
+        df[!, :a] .= length.(rhs)
+        @test size(df) == (0, 2)
+        @test eltype(df[!, 2]) == Int
+
+        df = DataFrame(x=Int[])
+        df[!, :a] .= length.(rhs) .+ 1
+        @test size(df) == (0, 2)
+        @test eltype(df[!, 2]) == Int
+
+        df = DataFrame(x=Int[])
+        @. df[!, :a] = length(rhs) + 1
+        @test size(df) == (0, 2)
+        @test eltype(df[!, 2]) == Int
+    end
+
+    df = DataFrame()
     df .= 1
     @test df == DataFrame()
     df .= [1]
@@ -615,11 +668,22 @@ end
     @test_throws DimensionMismatch df .= ones(1,2)
     @test_throws DimensionMismatch df .= ones(1,1,1)
 
-    @test_throws ArgumentError df[!, :a] .= 1
-    @test_throws ArgumentError df[!, [:a, :b]] .= 1
-
     df = DataFrame(a=[])
-    @test_throws ArgumentError df[!, :b] .= 1
+    df[!, :b] .= sin.(1)
+    @test eltype(df.b) == Float64
+    df[!, :b] .= [1]
+    @test eltype(df.b) == Int
+    df[!, :b] .= 'a'
+    @test eltype(df.b) == Char
+    @test names(df) == [:a, :b]
+
+    c = categorical(["a", "b", "c"])
+    df = DataFrame()
+    @test_throws DimensionMismatch df[!, :a] .= c
+
+    df[!, :b] .= c[1]
+    @test nrow(df) == 0
+    @test df.b isa CategoricalVector
 end
 
 @testset "test categorical values" begin
@@ -694,9 +758,11 @@ end
 
 @testset "scalar on assignment side" begin
     df = DataFrame(rand(2, 3))
-    df[1, 1] .= df[1, 1] .- df[1, 1]
+    @test_throws MethodError df[1, 1] .= df[1, 1] .- df[1, 1]
+    df[1, 1:1] .= df[1, 1] .- df[1, 1]
     @test df[1, 1] == 0
-    df[1, 2] .-= df[1, 2]
+    @test_throws MethodError df[1, 2] .-= df[1, 2]
+    df[1:1, 2] .-= df[1, 2]
     @test df[1, 2] == 0
 end
 
@@ -940,26 +1006,20 @@ end
 @testset "additional checks of post-! broadcasting rules" begin
     df = copy(refdf)
     v1 = df[!, 1]
-    df[CartesianIndex(1, 1)] .= VERSION >= v"1.1.0" ? 'd' : Ref('d')
-    @test v1 == [100.0, 2.5, 3.5]
+    @test_throws MethodError df[CartesianIndex(1, 1)] .= 1
     @test_throws MethodError df[CartesianIndex(1, 1)] .= "d"
-    @test v1 == [100.0, 2.5, 3.5]
     @test_throws DimensionMismatch df[CartesianIndex(1, 1)] .= [1,2]
 
     df = copy(refdf)
     v1 = df[!, 1]
-    df[1, 1] .= VERSION >= v"1.1.0" ? 'd' : Ref('d')
-    @test v1 == [100.0, 2.5, 3.5]
+    @test_throws MethodError df[1, 1] .= 1
     @test_throws MethodError df[1, 1] .= "d"
-    @test v1 == [100.0, 2.5, 3.5]
     @test_throws DimensionMismatch df[1, 1] .= [1, 2]
 
     df = copy(refdf)
     v1 = df[!, 1]
-    df[1, :x1] .= VERSION >= v"1.1.0" ? 'd' : Ref('d')
-    @test v1 == [100.0, 2.5, 3.5]
+    @test_throws MethodError df[1, :x1] .= 1
     @test_throws MethodError df[1, :x1] .= "d"
-    @test v1 == [100.0, 2.5, 3.5]
     @test_throws DimensionMismatch df[1, :x1] .= [1, 2]
 
     df = copy(refdf)
@@ -1088,7 +1148,7 @@ end
     @test df == refdf
     @test_throws ArgumentError df[!, 10] .= [1,2,3]
     @test df == refdf
-    @test_throws DimensionMismatch df[!, 10] .= [1 2 3]
+    @test_throws ArgumentError df[!, 10] .= [1 2 3]
     @test df == refdf
 
     df = copy(refdf)
@@ -1110,26 +1170,20 @@ end
 
     df = view(copy(refdf), :, :)
     v1 = df[!, 1]
-    df[CartesianIndex(1, 1)] .= VERSION >= v"1.1.0" ? 'd' : Ref('d')
-    @test v1 == [100.0, 2.5, 3.5]
+    @test_throws MethodError df[CartesianIndex(1, 1)] .= 1
     @test_throws MethodError df[CartesianIndex(1, 1)] .= "d"
-    @test v1 == [100.0, 2.5, 3.5]
     @test_throws DimensionMismatch df[CartesianIndex(1, 1)] .= [1,2]
 
     df = view(copy(refdf), :, :)
     v1 = df[!, 1]
-    df[1, 1] .= VERSION >= v"1.1.0" ? 'd' : Ref('d')
-    @test v1 == [100.0, 2.5, 3.5]
+    @test_throws MethodError df[1, 1] .= 1
     @test_throws MethodError df[1, 1] .= "d"
-    @test v1 == [100.0, 2.5, 3.5]
     @test_throws DimensionMismatch df[1, 1] .= [1, 2]
 
     df = view(copy(refdf), :, :)
     v1 = df[!, 1]
-    df[1, :x1] .= VERSION >= v"1.1.0" ? 'd' : Ref('d')
-    @test v1 == [100.0, 2.5, 3.5]
+    @test_throws MethodError df[1, :x1] .= 1
     @test_throws MethodError df[1, :x1] .= "d"
-    @test v1 == [100.0, 2.5, 3.5]
     @test_throws DimensionMismatch df[1, :x1] .= [1, 2]
 
     df = view(copy(refdf), :, :)
@@ -1277,4 +1331,18 @@ end
     @test df.a !== a
 end
 
+@testset "add new correct rules for df[row, col] .= v broadcasting" begin
+    df = DataFrame(a=1)
+    @test_throws MethodError df[1,1] .= 10
+    @test_throws MethodError df[1,:a] .= 10
+    @test_throws MethodError df[CartesianIndex(1,1)] .= 10
+    df = DataFrame(a=[[1,2,3]])
+    df[1,1] .= 10
+    @test df == DataFrame(a=[[10,10,10]])
+    df[1,:a] .= 100
+    @test df == DataFrame(a=[[100,100,100]])
+    df[CartesianIndex(1,1)] .= 1000
+    @test df == DataFrame(a=[[1000,1000,1000]])
+end
+
 end # module