Add support for map_keys_by_top_n_values

presto-docs/src/main/sphinx/functions/map.rst

@@ -121,6 +121,13 @@ Map Functions
 
         SELECT map_top_n_keys(map(ARRAY['a', 'b', 'c'], ARRAY[3, 2, 1]), 2, (x, y) -> IF(x < y, -1, IF(x = y, 0, 1))) --- ['c', 'b']
 
+.. function:: map_keys_by_top_n_values(x(K,V), n) -> array(K)
+
+    Returns top ``n`` keys in the map ``x`` by sorting its values in descending order. If two or more keys have equal values, the higher key takes precedence.
+    ``n`` must be a non-negative integer.
+
+        SELECT map_top_n_keys_by_value(map(ARRAY['a', 'b', 'c'], ARRAY[2, 1, 3]), 2) --- ['c', 'a']
+
 .. function:: map_top_n(x(K,V), n) -> map(K, V)
 
     Truncates map items. Keeps only the top N elements by value.

presto-main/src/main/java/com/facebook/presto/operator/scalar/sql/MapSqlFunctions.java

@@ -24,6 +24,17 @@ public class MapSqlFunctions
 {
     private MapSqlFunctions() {}
 
+    @SqlInvokedScalarFunction(value = "map_keys_by_top_n_values", deterministic = true, calledOnNullInput = false)
+    @Description("Returns the top N keys of the given map in descending order according to the natural ordering of its values.")
+    @TypeParameter("K")
+    @TypeParameter("V")
+    @SqlParameters({@SqlParameter(name = "input", type = "map(K, V)"), @SqlParameter(name = "n", type = "bigint")})
+    @SqlType("array<K>")
+    public static String mapKeysByTopNValues()
+    {
+        return "RETURN IF(n < 0, fail('n must be greater than or equal to 0'), map_keys(map_top_n(input, n)))";
+    }
+
     @SqlInvokedScalarFunction(value = "map_top_n", deterministic = true, calledOnNullInput = true)
     @Description("Truncates map items. Keeps only the top N elements by value.")
     @TypeParameter("K")
@@ -32,7 +43,7 @@ private MapSqlFunctions() {}
     @SqlType("map(K, V)")
     public static String mapTopN()
     {
-        return "RETURN IF(n < 0, fail('n must be greater than or equal to 0'), map_from_entries(slice(array_sort(map_entries(map_filter(input, (k, v) -> v is not null)), (x, y) -> IF(x[2] < y[2], 1, IF(x[2] = y[2], 0, -1))) || map_entries(map_filter(input, (k, v) -> v is null)), 1, n)))";
+        return "RETURN IF(n < 0, fail('n must be greater than or equal to 0'), map_from_entries(slice(array_sort(map_entries(map_filter(input, (k, v) -> v is not null)), (x, y) -> IF(x[2] < y[2], 1, IF(x[2] = y[2], IF(x[1] < y[1], 1, -1), -1))) || map_entries(map_filter(input, (k, v) -> v is null)), 1, n)))";
     }
 
     @SqlInvokedScalarFunction(value = "map_top_n_keys", deterministic = true, calledOnNullInput = false)

presto-main/src/test/java/com/facebook/presto/operator/scalar/sql/TestMapKeysByTopNValuesFunction.java

@@ -0,0 +1,124 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.facebook.presto.operator.scalar.sql;
+
+import com.facebook.presto.common.type.ArrayType;
+import com.facebook.presto.common.type.RowType;
+import com.facebook.presto.operator.scalar.AbstractTestFunctions;
+import com.facebook.presto.spi.StandardErrorCode;
+import com.google.common.collect.ImmutableList;
+import org.testng.annotations.Test;
+
+import static com.facebook.presto.common.type.DecimalType.createDecimalType;
+import static com.facebook.presto.common.type.IntegerType.INTEGER;
+import static com.facebook.presto.common.type.UnknownType.UNKNOWN;
+import static com.facebook.presto.common.type.VarcharType.createVarcharType;
+
+public class TestMapKeysByTopNValuesFunction
+        extends AbstractTestFunctions
+{
+    @Test
+    public void testBasic()
+    {
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[1, 2, 3], ARRAY[4, 5, 6]), 2)",
+                new ArrayType(INTEGER),
+                ImmutableList.of(3, 2));
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[-1, -2, -3], ARRAY[4, 5, 6]), 2)",
+                new ArrayType(INTEGER),
+                ImmutableList.of(-3, -2));
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY['ab', 'bc', 'cd'], ARRAY['x', 'y', 'z']), 1)",
+                new ArrayType(createVarcharType(2)),
+                ImmutableList.of("cd"));
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[123.0, 99.5, 1000.99], ARRAY['x', 'y', 'z']), 3)",
+                new ArrayType(createDecimalType(6, 2)),
+                ImmutableList.of(decimal("1000.99"), decimal("99.50"), decimal("123.00")));
+
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY['abc', 'cbc', 'cbd'], ARRAY[1, 1, 1]), 3)",
+                new ArrayType(createVarcharType(3)),
+                ImmutableList.of("cbd", "cbc", "abc"));
+
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY['ab', 'bc', 'cd', 'de', 'ee', 'ef', 'ac', 'ad'], ARRAY[1, 2, 2, 2, 4, 5, 5, 6]), 5)",
+                new ArrayType(createVarcharType(2)),
+                ImmutableList.of("ad", "ef", "ac", "ee", "de"));
+    }
+
+    @Test
+    public void testNegativeN()
+    {
+        assertInvalidFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[100, 200, 300], ARRAY[4, 5, 6]), -3)",
+                StandardErrorCode.GENERIC_USER_ERROR,
+                "n must be greater than or equal to 0");
+        assertInvalidFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[1, 2, 3], ARRAY[4, 5, 6]), -1)",
+                StandardErrorCode.GENERIC_USER_ERROR,
+                "n must be greater than or equal to 0");
+        assertInvalidFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY['a', 'b', 'c'], ARRAY[4, 5, 6]), -2)",
+                StandardErrorCode.GENERIC_USER_ERROR,
+                "n must be greater than or equal to 0");
+    }
+
+    @Test
+    public void testZeroN()
+    {
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[-1, -2, -3], ARRAY[4, 5, 6]), 0)",
+                new ArrayType(INTEGER),
+                ImmutableList.of());
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY['ab', 'bc', 'cd'], ARRAY['x', 'y', 'z']), 0)",
+                new ArrayType(createVarcharType(2)),
+                ImmutableList.of());
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[123.0, 99.5, 1000.99], ARRAY['x', 'y', 'z']), 0)",
+                new ArrayType(createDecimalType(6, 2)),
+                ImmutableList.of());
+    }
+
+    @Test
+    public void testEmpty()
+    {
+        assertFunction("MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[], ARRAY[]), 5)", new ArrayType(UNKNOWN), ImmutableList.of());
+    }
+
+    @Test
+    public void testNull()
+    {
+        assertFunction("MAP_KEYS_BY_TOP_N_VALUES(NULL, 1)", new ArrayType(UNKNOWN), null);
+    }
+
+    @Test
+    public void testComplexKeys()
+    {
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[ROW('x', 1), ROW('y', 2)], ARRAY[1, 2]), 1)",
+                new ArrayType(RowType.from(ImmutableList.of(RowType.field(createVarcharType(1)), RowType.field(INTEGER)))),
+                ImmutableList.of(ImmutableList.of("y", 2)));
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[ROW('x', 1), ROW('x', -2)], ARRAY[2, 1]), 1)",
+                new ArrayType(RowType.from(ImmutableList.of(RowType.field(createVarcharType(1)), RowType.field(INTEGER)))),
+                ImmutableList.of(ImmutableList.of("x", 1)));
+        assertFunction(
+                "MAP_KEYS_BY_TOP_N_VALUES(MAP(ARRAY[ROW('x', 1), ROW('x', -2), ROW('y', 1)], ARRAY[100, 200, null]), 3)",
+                new ArrayType(RowType.from(ImmutableList.of(RowType.field(createVarcharType(1)), RowType.field(INTEGER)))),
+                ImmutableList.of(ImmutableList.of("x", -2), ImmutableList.of("x", 1), ImmutableList.of("y", 1)));
+    }
+}