add view option for sorting views

Author: sl-solution

docs/src/man/tutorial.md

@@ -159,9 +159,9 @@ julia> delayed =  @chain flights begin
 
 ## Reorder rows
 
-Select `:IATA` and `:DepDelay` columns while sorted by `:DepDelay`. Note that in the following code, `flights[!, [:IATA, :DepDelay]]` is equivalent to `view(flights, :, [:IATA, :DepDelay])`. Further notice that calling `sort` on a view of a data set creates a new data set.
+Select `:IATA` and `:DepDelay` columns while sorted by `:DepDelay`. Note that in the following code, `flights[!, [:IATA, :DepDelay]]` is equivalent to `view(flights, :, [:IATA, :DepDelay])`. Further notice that, by default, calling `sort` on a view of a data set creates a new data set, however, passing `view = true` creates a view of sorted values.
 
-> Note `sort!` and `sort` reorder observations instead of sorting observations by reference (i.e. view of sorted data), however, we can use `groupby` or the combination of `sortperm` and `view` to create a sorting data set by reference.
+> Note `sort!` and `sort` reorder observations instead of sorting observations by reference (i.e. view of sorted data), however, we can use `groupby`, the combination of `sortperm` and `view`, or pass a view of a data set and set `view = true` to create a sorting data set by reference.
 
 
 ```julia

src/sort/sort.jl

@@ -87,7 +87,7 @@ end
 
 Base.sort(ds::Dataset, col::ColumnIndex; alg = HeapSortAlg(), rev::Bool = false, mapformats::Bool = true, stable =true) = sort(ds, [col], rev = rev, alg = alg, mapformats = mapformats, stable = stable)
 
-function Base.sort(ds::SubDataset, cols::MultiColumnIndex; alg = HeapSortAlg(), rev = false, mapformats::Bool = true, stable = true)
+function Base.sort(ds::SubDataset, cols::MultiColumnIndex; alg = HeapSortAlg(), rev = false, mapformats::Bool = true, stable = true, view = false)
     _check_consistency(ds)
     colsidx = index(ds)[cols]
     if rev isa AbstractVector
@@ -97,14 +97,18 @@ function Base.sort(ds::SubDataset, cols::MultiColumnIndex; alg = HeapSortAlg(),
         revs = repeat([rev], length(colsidx))
     end
     starts, idx, last_valid_range =  _sortperm_v(ds, cols, revs, stable = stable, a = alg, mapformats = mapformats)
-    newds = ds[idx, :]
-    append!(index(newds).sortedcols, collect(colsidx))
-    append!(index(newds).rev, revs)
-    append!(index(newds).perm, idx)
-    append!(index(newds).starts, starts)
-    index(newds).ngroups[] = last_valid_range
-    index(newds).fmt[] = mapformats
-    newds
+    if view
+        Base.view(ds, idx, :)
+    else
+        newds = ds[idx, :]
+        append!(index(newds).sortedcols, collect(colsidx))
+        append!(index(newds).rev, revs)
+        append!(index(newds).perm, idx)
+        append!(index(newds).starts, starts)
+        index(newds).ngroups[] = last_valid_range
+        index(newds).fmt[] = mapformats
+        newds
+    end
 end
 
 Base.sort(ds::SubDataset, col::ColumnIndex; alg = HeapSortAlg(), rev::Bool = false, mapformats::Bool = true, stable =true) = sort(ds, [col], rev = rev, alg = alg, mapformats = mapformats, stable = stable)