1- .. _kotlin-sync-sync- aggregation-expression-operations:
1+ .. _kotlin-sync-aggregation-expression-operations:
22
33=================================
44Aggregation Expression Operations
@@ -72,13 +72,13 @@ value of ``1.0``:
7272 of(1.0)
7373
7474To create an operation, chain a method to your field or value reference.
75- You can build more complex operations by chaining other methods.
75+ You can build more complex operations by chaining multiple methods.
7676
7777The following example creates an operation to find patients in New
7878Mexico who have visited the doctor’s office at least once. The operation
7979performs the following actions:
8080
81- - Checks if the size of the ``visitDates`` array is greater than ``0``
81+ - Checks if the size of the ``visitDates`` array value is greater than ``0``
8282 by using the ``gt()`` method
8383- Checks if the ``state`` field value is “New Mexico” by using the
8484 ``eq()`` method
@@ -112,11 +112,7 @@ how to include your expression in common aggregates builder methods:
112112- ``group(<expression>)``
113113
114114.. TODO To learn more about these methods, see the
115- .. :ref:`kotlin-sync-sync-aggregation`.
116-
117- The examples use the ``listOf()`` method to create a list of
118- aggregation stages. Then, the examples pass the pipeline to the
119- ``aggregate()`` method of ``MongoCollection``.
115+ .. :ref:`kotlin-sync-aggregation`.
120116
121117Constructor Methods
122118-------------------
@@ -195,6 +191,10 @@ the Server manual documentation. While each method is effectively
195191equivalent to the corresponding Query API expression, they may differ in
196192expected parameters and implementation.
197193
194+ The example in each section uses the ``listOf()`` method to create a
195+ pipeline from the aggregation stage. Then, each example passes the
196+ pipeline to the ``aggregate()`` method of ``MongoCollection``.
197+
198198.. note::
199199
200200 The driver generates a Query API expression that may be different
@@ -250,8 +250,8 @@ You can perform an arithmetic operation on a value of type ``MqlInteger`` or
250250 - :manual:`$subtract </reference/operator/aggregation/subtract/>`
251251
252252Suppose you have weather data for a specific year that includes the
253- precipitation measurement (in inches) for each day. You want find the average
254- precipitation, in millimeters, for each month.
253+ precipitation measurement (in inches) for each day. You want to find the
254+ average precipitation, in millimeters, for each month.
255255
256256The ``multiply()`` operator multiplies the ``precipitation`` field by
257257``25.4`` to convert the value to millimeters. The ``avg()`` accumulator method
@@ -389,18 +389,20 @@ following:
389389The ``filter()`` method displays only the results matching the provided
390390predicate. In this case, the predicate uses ``sum()`` to calculate the
391391total number of seats and compares that value to the number of ``ticketsBought``
392- with ``lt()``. The ``project()`` method stores these filtered results as a new
393- ``availableShowtimes`` array.
392+ by using the ``lt()`` method . The ``project()`` method stores these
393+ filtered results as a new ``availableShowtimes`` array field .
394394
395395.. tip::
396396
397- You must specify the type of the array that you retrieve with the
398- ``getArray()`` method if you work with the values of the
399- array as their specific type.
397+ You must specify the type of values that an array contains when using
398+ the ``getArray()`` method to work with the values as any specific
399+ type. For example, you must specify that an array contains integers
400+ if you want to perform calculations with those integers elsewhere in
401+ your application.
400402
401- In this example, we specify that the ``seats`` array contains values
402- of type ``MqlDocument`` so that we can extract nested fields from
403- each array entry.
403+ The example in this section specifies that the ``seats`` array
404+ contains values of type ``MqlDocument`` so that it can extract nested
405+ fields from each array entry.
404406
405407The following code shows the pipeline for this aggregation:
406408
@@ -414,8 +416,8 @@ The following code shows the pipeline for this aggregation:
414416.. note::
415417
416418 To improve readability, the previous example assigns intermediary values to
417- the ``totalSeats`` and ``isAvailable`` variables. If you don't pull
418- out these intermediary values into variables, the code still produces
419+ the ``totalSeats`` and ``isAvailable`` variables. If you don't assign
420+ these intermediary values to variables, the code still produces
419421 equivalent results.
420422
421423The following code provides an equivalent aggregation pipeline in
@@ -459,8 +461,9 @@ Suppose you want to classify very low or high weather temperature
459461readings (in degrees Fahrenheit) as extreme.
460462
461463The ``or()`` operator checks to see if temperatures are extreme by comparing
462- the ``temperature`` field to predefined values with ``lt()`` and ``gt()``.
463- The ``project()`` method records this result in the ``extremeTemp`` field.
464+ the ``temperature`` field to predefined values by using the ``lt()`` and
465+ ``gt()`` methods. The ``project()`` method records this result in the
466+ ``extremeTemp`` field.
464467
465468The following code shows the pipeline for this aggregation:
466469
@@ -675,13 +678,12 @@ how the values compare:
675678
676679.. tip::
677680
678- One advantage of using the ``passTo()`` method is that you can reuse
679- your custom methods for other aggregations. You could
681+ Using the ``passTo()`` method allows you to reuse
682+ your custom methods for other aggregations. For example, you can
680683 use the ``gradeAverage()`` method to find the average of grades for
681684 groups of students filtered by entry year or district, not just their
682- class, for example. You could use the ``evaluate()`` method to evaluate, for
683- example, an individual student's performance, or an entire school's or
684- district's performance.
685+ class. Similarly, you could use the ``evaluate()`` method to evaluate
686+ an individual student's performance or an entire school's performance.
685687
686688The ``passArrayTo()`` method takes an array of all students and calculates the
687689average score by using the ``gradeAverage()`` method. Then, the
@@ -832,10 +834,10 @@ valid dates, such as ``"2018-01-15T16:00:00Z"`` or ``"Jan 15, 2018, 12:00
832834PM EST"``, you can use the ``parseDate()`` method to convert the strings
833835into date types.
834836
835- The ``dayOfWeek()`` method determines which day of the week it is and converts
836- it to a number based on which day is a Monday according to the
837- ``"America/New_York"`` parameter . The ``eq()`` method compares this value to
838- ``2``, which corresponds to Monday based on the provided timezone parameter .
837+ The ``dayOfWeek()`` method determines which day of the week that a date
838+ is, then converts it to a number. The number assignment uses ``0`` to mean
839+ Sunday when using the ``"America/New_York"`` timezone . The ``eq()``
840+ method compares this value to ``2``, or Monday.
839841
840842The following code shows the pipeline for this aggregation:
841843
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