check for data frame corruption in delete!

NEWS.md

@@ -33,6 +33,8 @@
   selected as a property (e.g. `df.col .= 1`) is allowed when column does not
   exist and it allocates a fresh column
   ([#2655](https://github.com/JuliaData/DataFrames.jl/pull/2655))
+* `delete!` now correctly handles the case when columns of a data frame are aliased
+  ([#2690](https://github.com/JuliaData/DataFrames.jl/pull/2690))
 
 ## Deprecated
 

src/dataframe/dataframe.jl

@@ -966,23 +966,46 @@ function Base.delete!(df::DataFrame, inds)
     if !isempty(inds) && size(df, 2) == 0
         throw(BoundsError(df, (inds, :)))
     end
+
     # we require ind to be stored and unique like in Base
     # otherwise an error will be thrown and the data frame will get corrupted
-    foreach(col -> deleteat!(col, inds), _columns(df))
-    return df
+    return _delete!_helper(df, inds)
 end
 
 function Base.delete!(df::DataFrame, inds::AbstractVector{Bool})
     if length(inds) != size(df, 1)
         throw(BoundsError(df, (inds, :)))
     end
     drop = findall(inds)
-    foreach(col -> deleteat!(col, drop), _columns(df))
-    return df
+    return _delete!_helper(df, drop)
 end
 
 Base.delete!(df::DataFrame, inds::Not) = delete!(df, axes(df, 1)[inds])
 
+function _delete!_helper(df::DataFrame, drop)
+    cols = _columns(df)
+    isempty(cols) && return df
+
+    n = nrow(df)
+    col1 = cols[1]
+    deleteat!(col1, drop)
+    newn = length(col1)
+
+    for i in 2:length(cols)
+        col = cols[i]
+        if length(col) == n
+            deleteat!(col, drop)
+        end
+    end
+
+    for i in 1:length(cols)
+        # this should never happen, but we add it for safety
+        @assert length(cols[i]) == newn corrupt_msg(df, i)
+    end
+
+    return df
+end
+
 """
     empty!(df::DataFrame)
 

test/dataframe.jl

@@ -613,6 +613,17 @@ end
         @test delete!(df, v) == DataFrame(x=[2, 3])
         @test x == [2, 3]
     end
+
+    for inds in (1, [1], [true, false])
+        df = DataFrame(x1=[1, 2])
+        df.x2 = df.x1
+        @test delete!(df, inds) === df
+        @test df == DataFrame(x1=[2], x2=[2])
+    end
+
+    df = DataFrame(a=1, b=2)
+    push!(df.b, 3)
+    @test_throws AssertionError delete!(df, 1)
 end
 
 @testset "describe" begin