mapcols!(): exit early if no columns

fixes #2474
JuliaData · Oct 9, 2020 · 48c3032 · 48c3032
1 parent 4ec8009
commit 48c3032
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diff --git a/src/abstractdataframe/iteration.jl b/src/abstractdataframe/iteration.jl
@@ -411,6 +411,8 @@ julia> df
 """
 function mapcols!(f::Union{Function,Type}, df::DataFrame)
     # note: `f` must return a consistent length
+    (ncol(df) == 0) && return df # skip if no columns
+
     vs = AbstractVector[]
     seenscalar = false
     seenvector = false

diff --git a/test/iteration.jl b/test/iteration.jl
@@ -71,8 +71,11 @@ end
 end
 
 @testset "mapcols!" begin
+    df_empty = DataFrame()
+    @test mapcols!(sum, df_empty) === df_empty
+
     df_mapcols = DataFrame(a=1:10, b=11:20)
-    mapcols!(sum, df_mapcols)
+    @test mapcols!(sum, df_mapcols) === df_mapcols
     @test df_mapcols == DataFrame(a=55, b=155)
 
     df_mapcols = DataFrame(a=1:10, b=11:20)