adjust outer join behavior (types and right outer join bug)

outer joins need to return nullable tables as they may introduce missing
data. similar_nullable on DataTables has been removed (unused) and
replaced with a similar_nullable that works on
NullableCategoricalArrays, and this change is made to support the new
changes to join. The 3 outer joins share a function with inner joins,
and this shared function (compose_joined_table) now performs a check to
see if the join type is :inner, and if so, it will return the same
column type as the parent table rather than promoting to a nullable
column. A bug was found in right-outer join behavior where the values
unique to the right table were added to the table in the incorrect
locations, overwriting data and leaving nulls where they shouldn't be.
This bug, due to incorrect values in rightonly_ixs.join, was fixed by
filling the last n-rows of the datatable where n =
length(rightonly_ixs.join). Tests were checked for accuracy against
pandas.

src/abstractdatatable/join.jl

@@ -9,13 +9,10 @@ similar_nullable{T}(dv::AbstractArray{T}, dims::Union{Int, Tuple{Vararg{Int}}})
 similar_nullable{T<:Nullable}(dv::AbstractArray{T}, dims::Union{Int, Tuple{Vararg{Int}}}) =
     NullableArray{eltype(T)}(dims)
 
-similar_nullable{T,R}(dv::CategoricalArray{T,R}, dims::Union{Int, Tuple{Vararg{Int}}}) =
+similar_nullable{T}(dv::CategoricalArray{T}, dims::Union{Int, Tuple{Vararg{Int}}}) =
     NullableCategoricalArray{T}(dims)
 
-similar_nullable(dt::AbstractDataTable, dims::Int) =
-    DataTable(Any[similar_nullable(x, dims) for x in columns(dt)], copy(index(dt)))
-
-similar_nullable{T,R}(dv::NullableCategoricalArray{T,R}, dims::Union{Int, Tuple{Vararg{Int}}}) =
+similar_nullable{T}(dv::NullableCategoricalArray{T}, dims::Union{Int, Tuple{Vararg{Int}}}) =
     NullableCategoricalArray{T}(dims)
 
 # helper structure for DataTables joining
@@ -47,55 +44,74 @@ Base.length(x::RowIndexMap) = length(x.orig)
 
 # composes the joined data table using the maps between the left and right
 # table rows and the indices of rows in the result
-function compose_joined_table(joiner::DataTableJoiner,
+function compose_joined_table(joiner::DataTableJoiner, kind::Symbol,
                               left_ixs::RowIndexMap, leftonly_ixs::RowIndexMap,
                               right_ixs::RowIndexMap, rightonly_ixs::RowIndexMap)
     @assert length(left_ixs) == length(right_ixs)
     # compose left half of the result taking all left columns
     all_orig_left_ixs = vcat(left_ixs.orig, leftonly_ixs.orig)
-    if length(leftonly_ixs) > 0
+
+    ril = length(right_ixs)
+    lil = length(left_ixs)
+    loil = length(leftonly_ixs)
+    roil = length(rightonly_ixs)
+
+    if loil > 0
         # combine the matched (left_ixs.orig) and non-matched (leftonly_ixs.orig) indices of the left table rows
         # preserving the original rows order
-        all_orig_left_ixs = similar(left_ixs.orig, length(left_ixs)+length(leftonly_ixs))
+        all_orig_left_ixs = similar(left_ixs.orig, lil + loil)
         @inbounds all_orig_left_ixs[left_ixs.join] = left_ixs.orig
         @inbounds all_orig_left_ixs[leftonly_ixs.join] = leftonly_ixs.orig
     else
         # the result contains only the left rows that are matched to right rows (left_ixs)
         all_orig_left_ixs = left_ixs.orig # no need to copy left_ixs.orig as it's not used elsewhere
     end
-    ril = length(right_ixs)
-    loil = length(leftonly_ixs)
-    roil = length(rightonly_ixs)
-    left_dt = DataTable(Any[resize!(col[all_orig_left_ixs], length(all_orig_left_ixs)+roil)
-                            for col in columns(joiner.dtl)],
-                        names(joiner.dtl))
-
-    # compose right half of the result taking all right columns excluding on
-    dtr_noon = without(joiner.dtr, joiner.on_cols)
     # permutation to swap rightonly and leftonly rows
     right_perm = vcat(1:ril, ril+roil+1:ril+roil+loil, ril+1:ril+roil)
     if length(leftonly_ixs) > 0
         # compose right_perm with the permutation that restores left rows order
         right_perm[vcat(right_ixs.join, leftonly_ixs.join)] = right_perm[1:ril+loil]
     end
     all_orig_right_ixs = vcat(right_ixs.orig, rightonly_ixs.orig)
-    right_dt = DataTable(Any[resize!(col[all_orig_right_ixs], length(all_orig_right_ixs)+loil)[right_perm]
-                             for col in columns(dtr_noon)],
-                         names(dtr_noon))
-    # merge left and right parts of the joined table
-    res = hcat!(left_dt, right_dt)
+
+    # compose right half of the result taking all right columns excluding on
+    dtr_noon = without(joiner.dtr, joiner.on_cols)
+
+    nrow = length(all_orig_left_ixs) + roil
+    @assert nrow == length(all_orig_right_ixs) + loil
+    ncleft = ncol(joiner.dtl)
+    cols = Vector{Any}(ncleft + ncol(dtr_noon))
+    _similar = kind == :inner ? similar : similar_nullable
+    for (i, col) in enumerate(columns(joiner.dtl))
+        cols[i] = _similar(col, nrow)
+        fillcolumn!(cols[i], col, all_orig_left_ixs)
+    end
+    for (i, col) in enumerate(columns(dtr_noon))
+        cols[i+ncleft] = _similar(col, nrow)
+        fillcolumn!(cols[i+ncleft], col, all_orig_right_ixs)
+        permute!(cols[i+ncleft], right_perm)
+    end
+    res = DataTable(cols, vcat(names(joiner.dtl), names(dtr_noon)))
 
     if length(rightonly_ixs.join) > 0
         # some left rows are nulls, so the values of the "on" columns
         # need to be taken from the right
         for (on_col_ix, on_col) in enumerate(joiner.on_cols)
             # fix the result of the rightjoin by taking the nonnull values from the right table
-            res[on_col][rightonly_ixs.join] = joiner.dtr_on[rightonly_ixs.orig, on_col_ix]
+            offset = nrow - length(rightonly_ixs.orig)
+            fillcolumn!(res[on_col], joiner.dtr_on[on_col_ix], rightonly_ixs.orig, offset)
         end
     end
     return res
 end
 
+function fillcolumn!{T1, T2}(dtcol::AbstractVector{T1}, refcol::AbstractVector{T2},
+                             indices::Vector{Int}, offset::Int=0)
+    @inbounds for (j, k) in enumerate(indices)
+        dtcol[j+offset] = refcol[k]
+    end
+end
+
 # map the indices of the left and right joined tables
 # to the indices of the rows in the resulting table
 # if `nothing` is given, the corresponding map is not built
@@ -210,7 +226,8 @@ join(dt1::AbstractDataTable,
   - `:cross` : a full Cartesian product of the key combinations; every
     row of `dt1` is matched with every row of `dt2`
 
-Null values are filled in where needed to complete joins.
+For the three join operations that may introduce missing values (`:outer`, `:left`,
+and `:right`), all columns of the returned data table will be nullable.
 
 ### Result
 
@@ -246,22 +263,21 @@ function Base.join(dt1::AbstractDataTable,
     joiner = DataTableJoiner(dt1, dt2, on)
 
     if kind == :inner
-        compose_joined_table(joiner, update_row_maps!(joiner.dtl_on, joiner.dtr_on,
-                                                      group_rows(joiner.dtr_on),
-                                                      true, false, true, false)...)
+        compose_joined_table(joiner, kind, update_row_maps!(joiner.dtl_on, joiner.dtr_on,
+                                                            group_rows(joiner.dtr_on),
+                                                            true, false, true, false)...)
     elseif kind == :left
-        compose_joined_table(joiner, update_row_maps!(joiner.dtl_on, joiner.dtr_on,
-                                                      group_rows(joiner.dtr_on),
-                                                      true, true, true, false)...)
+        compose_joined_table(joiner, kind, update_row_maps!(joiner.dtl_on, joiner.dtr_on,
+                                                            group_rows(joiner.dtr_on),
+                                                            true, true, true, false)...)
     elseif kind == :right
-        right_ixs, rightonly_ixs, left_ixs, leftonly_ixs = update_row_maps!(joiner.dtr_on, joiner.dtl_on,
-                                                                            group_rows(joiner.dtl_on),
-                                                                            true, true, true, false)
-        compose_joined_table(joiner, left_ixs, leftonly_ixs, right_ixs, rightonly_ixs)
+        compose_joined_table(joiner, kind, update_row_maps!(joiner.dtr_on, joiner.dtl_on,
+                                                            group_rows(joiner.dtl_on),
+                                                            true, true, true, false)[[3, 4, 1, 2]]...)
     elseif kind == :outer
-        compose_joined_table(joiner, update_row_maps!(joiner.dtl_on, joiner.dtr_on,
-                                                      group_rows(joiner.dtr_on),
-                                                      true, true, true, true)...)
+        compose_joined_table(joiner, kind, update_row_maps!(joiner.dtl_on, joiner.dtr_on,
+                                                            group_rows(joiner.dtr_on),
+                                                            true, true, true, true)...)
     elseif kind == :semi
         # hash the right rows
         dtr_on_grp = group_rows(joiner.dtr_on)