first_n, last_n, max_n and min_n reductions

datashader/compiler.py

@@ -164,14 +164,20 @@ def make_append(bases, cols, calls, glyph, categorical, antialias):
         if antialias:
             args.append("aa_factor")
 
-        body.append('{0}(x, y, {1})'.format(func_name, ', '.join(args)))
-
         where_reduction = len(bases) == 1 and isinstance(bases[0], where)
         if where_reduction:
+            update_index_arg_name = next(names)
+            args.append(update_index_arg_name)
+
             # where reduction needs access to the return of the contained
             # reduction, which is the preceding one here.
-            body[-2] = 'if ' + body[-2] + ' >= 0:'
-            body[-1] = '    ' + body[-1]
+            body[-1] = f'{update_index_arg_name} = {body[-1]}'
+            body.append(f'if {update_index_arg_name} >= 0:')
+            call  = '    {0}(x, y, {1})'.format(func_name, ', '.join(args))
+        else:
+            call  = '{0}(x, y, {1})'.format(func_name, ', '.join(args))
+
+        body.append(call)
 
     body = ['{0} = {1}[y, x]'.format(name, arg_lk[agg])
             for agg, name in local_lk.items()] + body

datashader/core.py

@@ -442,7 +442,7 @@ def line(self, source, x=None, y=None, agg=None, axis=0, geometry=None,
 
             if not isinstance(non_cat_agg, (
                 rd.any, rd.count, rd.max, rd.min, rd.sum, rd.summary, rd._sum_zero,
-                rd.first, rd.last, rd.mean, rd.where
+                rd.first, rd.last, rd.mean
             )):
                 raise NotImplementedError(
                     f"{type(non_cat_agg)} reduction not implemented for antialiased lines")
@@ -1312,16 +1312,19 @@ def _cols_to_keep(columns, glyph, agg):
     for col in glyph.required_columns():
         cols_to_keep[col] = True
 
-    if hasattr(agg, 'values'):
-        for subagg in agg.values:
-            if subagg.column is not None:
-                cols_to_keep[subagg.column] = True
-    elif hasattr(agg, 'columns'):
-        for column in agg.columns:
-            if column is not None:
-                cols_to_keep[column] = True
-    elif agg.column is not None:
-        cols_to_keep[agg.column] = True
+    def recurse(cols_to_keep, agg):
+        if hasattr(agg, 'values'):
+            for subagg in agg.values:
+                recurse(cols_to_keep, subagg)
+        elif hasattr(agg, 'columns'):
+            for column in agg.columns:
+                if column is not None:
+                    cols_to_keep[column] = True
+        elif agg.column is not None:
+            cols_to_keep[agg.column] = True
+
+    recurse(cols_to_keep, agg)
+
     return [col for col, keepit in cols_to_keep.items() if keepit]
 
 

datashader/glyphs/line.py

@@ -1096,11 +1096,9 @@ def _aa_stage_2_clear(aggs_and_copies, antialias_zeroes):
 
 @ngjit
 def _aa_stage_2_copy_back(aggs_and_copies):
-    k = 0
     # Numba access to heterogeneous tuples is only permitted using literal_unroll.
     for agg_and_copy in literal_unroll(aggs_and_copies):
         agg_and_copy[0][:] = agg_and_copy[1][:]
-        k += 1
 
 
 def _build_extend_line_axis0_multi(draw_segment, expand_aggs_and_cols, use_2_stage_agg):