Expand documentation for map_agg (#6911)

Summary:
Clarify that inputs with NULL or duplicate keys are ignored.

Pull Request resolved: #6911

Reviewed By: xiaoxmeng

Differential Revision: D49954059

Pulled By: mbasmanova

fbshipit-source-id: ad054d79acc2045724050685e15a97abbbba3515

velox/docs/functions/presto/aggregate.rst

@@ -17,11 +17,11 @@ depending on the order of input values.
 General Aggregate Functions
 ---------------------------
 
-.. function:: arbitrary(x) -> [same as input]
+.. function:: arbitrary(x) -> [same as x]
 
     Returns an arbitrary non-null value of ``x``, if one exists.
 
-.. function:: array_agg(x) -> array<[same as input]>
+.. function:: array_agg(x) -> array<[same as x]>
 
     Returns an array created from the input ``x`` elements. Ignores null
     inputs if :doc:`presto.array_agg.ignore_nulls <../../configs>` is set
@@ -93,6 +93,7 @@ General Aggregate Functions
     Returns the value of ``x`` associated with the maximum value of ``y`` over all input values.
 
 .. function:: max_by(x, y, n) -> array([same as x])
+    :noindex:
 
     Returns n values of ``x`` associated with the n largest values of ``y`` in descending order of ``y``.
 
@@ -101,30 +102,33 @@ General Aggregate Functions
     Returns the value of ``x`` associated with the minimum value of ``y`` over all input values.
 
 .. function:: min_by(x, y, n) -> array([same as x])
+    :noindex:
 
     Returns n values of ``x`` associated with the n smallest values of ``y`` in ascending order of ``y``.
 
-.. function:: max(x) -> [same as input]
+.. function:: max(x) -> [same as x]
 
     Returns the maximum value of all input values.
     ``x`` must not contain nulls when it is complex type.
 
 .. function:: max(x, n) -> array<[same as x]>
+    :noindex:
 
     Returns ``n`` largest values of all input values of ``x``.
     ``n`` must be a positive integer and not exceed 10'000.
 
-.. function:: min(x) -> [same as input]
+.. function:: min(x) -> [same as x]
 
     Returns the minimum value of all input values.
     ``x`` must not contain nulls when it is complex type.
 
 .. function:: min(x, n) -> array<[same as x]>
+    :noindex:
 
     Returns ``n`` smallest values of all input values of ``x``.
     ``n`` must be a positive integer and not exceed 10'000.
 
-.. function:: multimap_agg(key, value) -> map(K,array(V))
+.. function:: multimap_agg(K key, V value) -> map(K,array(V))
 
     Returns a multimap created from the input ``key`` / ``value`` pairs.
     Each key can be associated with multiple values.
@@ -190,7 +194,7 @@ General Aggregate Functions
         -- (1, 3.0)
         -- (2, 30.0)
 
-.. function:: set_agg(x) -> array<[same as input]>
+.. function:: set_agg(x) -> array<[same as x]>
 
     Returns an array created from the distinct input ``x`` elements.
     ``x`` must not contain nulls when it is complex type.
@@ -212,7 +216,7 @@ General Aggregate Functions
 
     Returns ARRAY[1, 2, 3, 4]
 
-.. function:: sum(x) -> [same as input]
+.. function:: sum(x) -> [same as x]
 
     Returns the sum of all input values.
 
@@ -227,7 +231,7 @@ Bitwise Aggregate Functions
 
     Returns the bitwise OR of all input values in 2's complement representation.
 
-.. function:: bitwise_xor_agg(x) -> [same as input]
+.. function:: bitwise_xor_agg(x) -> [same as x]
 
     Returns the bitwise XOR of all input values in 2's complement representation.
 
@@ -236,9 +240,9 @@ Bitwise Aggregate Functions
 Map Aggregate Functions
 -----------------------
 
-.. function:: map_agg(key, value) -> map(K,V)
+.. function:: map_agg(K key, V value) -> map(K,V)
 
-    Returns a map created from the input ``key`` / ``value`` pairs.
+    Returns a map created from the input ``key`` / ``value`` pairs. Inputs with NULL or duplicate keys are ignored.
 
 .. function:: map_union(map(K,V)) -> map(K,V)