DOCSP-14384 fix first last accumulators (#2231)

* Removed first and last array operator topics

* Removed links to  and  array operator topics

* Added array behavior to existing  and  topics

* Cleaned up links

* Removed includes, started work on making ref sections consistent

* Fixed aggregation accumulators landing page entries for first and last

* Fixed descriptions for first and last

* PR feedback and testing a ref

* Updates to link cleanup

* Reduced number of links per style guidelines

* Parallel cleanup on headings and structure

* Latest cleanup on  and

* Fixed firstN summary in aggregation reference

* Committing cleaned branch

* Restoring first/last updates to manually back out time series changes

* Removed draft content for time series changes

* Added first/last accumulator links to ArrayElemAt to replace expression links

* Rebuilding

Author: nvillahermosa-mdb

source/includes/extracts-agg-operators.yaml

@@ -177,10 +177,6 @@ content: |
         - Selects a subset of the array to return an array with only
           the elements that match the filter condition.
 
-      * - :expression:`$first`
-
-        - Returns the first array element. Distinct from :group:`$first` accumulator.
-
       * - :expression:`$firstN`
 
         - Returns a specified number of elements from the beginning of an array.
@@ -201,10 +197,6 @@ content: |
 
         - Determines if the operand is an array. Returns a boolean.
 
-      * - :expression:`$last`
-
-        - Returns the last array element. Distinct from :group:`$last` accumulator.
-
       * - :expression:`$lastN`
 
         - Returns a specified number of elements from the end of an array.
@@ -1061,10 +1053,8 @@ content: |
 
       * - :group:`$first`
 
-        - Returns a value from the first document for each group. Order
-          is only defined if the documents are sorted.
-          
-          Distinct from the :expression:`$first` array operator.
+        - Returns the result of an :ref:`expression
+          <aggregation-expressions>` for the first document in a group.
 
           .. versionchanged:: 5.0
 
@@ -1084,10 +1074,8 @@ content: |
 
       * - :group:`$last`
 
-        - Returns a value from the last document for each group. Order
-          is only defined if the documents are sorted.
-          
-          Distinct from the :expression:`$last` array operator.
+        - Returns the result of an :ref:`expression
+          <aggregation-expressions>` for the last document in a group.
 
           .. versionchanged:: 5.0
 
@@ -1213,6 +1201,16 @@ content: |
         - Returns an average of the specified expression or list of
           expressions for each document. Ignores non-numeric values.
 
+      * - :group:`$first`
+
+        - Returns the result of an :ref:`expression
+          <aggregation-expressions>` for the first document in a group.
+
+      * - :group:`$last`
+
+        - Returns the result of an :ref:`expression
+          <aggregation-expressions>` for the last document in a group.
+
       * - :group:`$max`
 
         - Returns the maximum of the specified expression or list of
@@ -1352,9 +1350,9 @@ content: |
 
       * - :group:`$first`
 
-        - Returns the value that results from applying an
-          :ref:`expression <aggregation-expressions>` to the first
-          document in a group or :ref:`window <setWindowFields-window>`.
+        - Returns the result of an :ref:`expression
+          <aggregation-expressions>` for the first document in a group
+          or :ref:`window <setWindowFields-window>`.
 
           .. versionchanged:: 5.0
 
@@ -1368,9 +1366,9 @@ content: |
 
       * - :group:`$last`
 
-        - Returns the value that results from applying an
-          :ref:`expression <aggregation-expressions>` to the last
-          document in a group or :ref:`window <setWindowFields-window>`.
+        - Returns the result of an :ref:`expression
+          <aggregation-expressions>` for the last document in a group
+          or :ref:`window <setWindowFields-window>`.
         
           .. versionchanged:: 5.0
 

source/includes/note-group-and-window-behavior.rst

@@ -376,8 +376,7 @@ Index of Expression Operators
    - :expression:`$eq`
    - :expression:`$exp`
    - :expression:`$filter`
-   - :expression:`$first` (array)
-   - :group:`$first` (accumulator)
+   - :group:`$first`
    - :expression:`$floor`
    - :expression:`$function`
    - :expression:`$getField`
@@ -394,8 +393,7 @@ Index of Expression Operators
    - :expression:`$isoDayOfWeek`
    - :expression:`$isoWeek`
    - :expression:`$isoWeekYear`
-   - :expression:`$last` (array)
-   - :group:`$last` (accumulator)
+   - :group:`$last`
    - :expression:`$let`
    - :expression:`$literal`
    - :expression:`$ln`

source/meta/aggregation-quick-reference.txt

@@ -15,8 +15,8 @@ Definition
 
 .. dbcommand:: collMod
 
-   :dbcommand:`collMod` makes it possible to add options to a collection
-   or to modify view definitions.
+   :dbcommand:`collMod` makes it possible to add options to a 
+   collection or to modify view definitions.
 
    .. |method| replace:: :method:`~db.collection.hideIndex` and
       :method:`~db.collection.unhideIndex` helper methods

source/reference/command/collMod.txt

@@ -502,31 +502,19 @@ Alphabetical Listing of Expression Operators
        .. versionchanged:: 5.0
 
           Available in :pipeline:`$setWindowFields` stage.
-   
-       Distinct from the :expression:`$first` array operator.
-
-
-   * - :expression:`$first`
-
-     - Returns the first array element.
-   
-       .. versionadded:: 4.4
-   
-       Distinct from the :group:`$first` accumulator.
 
    * - :expression:`$firstN`
 
      - Returns a specified number of elements from the beginning of an 
-       array.
-       Distinct from the :group:`$firstN` accumulator.
+       array. Distinct from the :group:`$firstN` accumulator.
 
        .. versionadded:: 5.2
 
    * - :group:`$firstN`
 
      - Returns an aggregation of the first ``n`` fields within a group.
-       Only meaningful when documents are in a defined order.
-       Distinct from the :expression:`$firstN` array operator.
+       Results are only meaningful when documents are in a defined
+       order. Distinct from the :expression:`$firstN` array operator.
 
        .. versionadded:: 5.2
 
@@ -654,17 +642,7 @@ Alphabetical Listing of Expression Operators
        .. versionchanged:: 5.0
 
           Available in :pipeline:`$setWindowFields` stage.
-   
-       Distinct from the :expression:`$last` array operator.
-   
-
-   * - :expression:`$last`
 
-     - Returns the last array element.
-      
-       .. versionadded:: 4.4
-   
-       Distinct from the :group:`$last` accumulator.
 
    * - :expression:`$lastN`
 
@@ -676,8 +654,8 @@ Alphabetical Listing of Expression Operators
    * - :group:`$lastN`
 
      - Returns an aggregation of the last ``n`` fields within a group.
-       Only meaningful when documents are in a defined order.
-       Distinct from the :expression:`$lastN` array operator.
+       Results are only meaningful when documents are in a defined
+       order. Distinct from the :expression:`$lastN` array operator.
 
        .. versionadded:: 5.2
 
@@ -1336,7 +1314,6 @@ Alphabetical Listing of Expression Operators
    /reference/operator/aggregation/filter
    /reference/operator/aggregation/first
    /reference/operator/aggregation/firstN
-   /reference/operator/aggregation/first-array-element
    /reference/operator/aggregation/firstN-array-element
    /reference/operator/aggregation/floor
    /reference/operator/aggregation/function
@@ -1357,7 +1334,6 @@ Alphabetical Listing of Expression Operators
    /reference/operator/aggregation/isoWeekYear
    /reference/operator/aggregation/last
    /reference/operator/aggregation/lastN
-   /reference/operator/aggregation/last-array-element
    /reference/operator/aggregation/lastN-array-element
    /reference/operator/aggregation/let
    /reference/operator/aggregation/linearFill

source/reference/operator/aggregation.txt

@@ -110,10 +110,10 @@ The operation returns the following results:
 See Also
 --------
 
-- :expression:`$first`
+- :expression:`$slice`
 
-- :expression:`$last`
+- :group:`$first`
 
-- :expression:`$slice`
+- :group:`last`
 
 - :ref:`agg-quick-ref-operator-array`