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agg [r] [[gc] GROUPING_FUNCTION] INITIAL_VALUE
AGGREGATION_FUNCTION
Aggregates objects from the input stream. If
GROUPING_FUNCTION
is omitted, then one output object is
generated by initializing an accumulator to INITIAL_VALUE
and then combining the accumulator with input objects using
AGGREGATION_FUNCTION
. AGGREGATION_FUNCTION
takes two inputs, the current value of the accumulator and an object from
the input stream.
Example: If the input objects are integers 1, 2, 3
, then
the sum of the integers is computed as follows:
... ^ agg 0 'sum, x: sum + x'
which yields (6,)
.
If GROUPING_FUNCTION
is specified, then a set of
accumulators is maintained, one for each value of
GROUPING_FUNCTION
. Each output object is a tuple with two
parts, the group value and the accumulated value for the group.
Example: If the input objects are ('a', 1), ('a', 2), ('b', 3),
('b', 4)
, then the sum of ints for each string is computed as
follows:
... ^ agg g 'x, y: x' 0 'sum, x, y: sum + y'
which yields ('a', 3), ('b', 7)
.
If the grouping function is specified with the g
flag,
then agg generates its output when the input stream has ended. (It has
to, because group members map appear in any order.) In some situations
however, group members appear consecutively, and it is useful to get
output earlier. If group members are known to be consecutive, then the
group function can be specified using the c
flag.
If the r
flag is specified, then one output object is
generated for each input object; the output object contains the value of
the accumulator so far. The accumulator appears in the output row before
the inputs. For example, if the input stream contains 1, 2,
3
, then the running total can be computed as follows:
... ^ agg r 0 'sum, x: sum + x' ^ ...
The output stream would be (1, 1), (3, 2), (6, 3)
. In the
last output object, 6
is the sum of the current input
(3
) and all preceding inputs (1, 2
).
The r
flag can also be used with grouping. For example,
if the input objects are ('a', 1), ('a', 2), ('b', 3), ('b',
4)
, then the running totals for the strings would be computed as
follows:
... ^ agg r g 'x, y: x' 0 'sum, x, y: sum + y' ^ ...
The output stream would be (1, 'a', 1), (3, 'a', 2), (3, 'b',
3), (7, 'b', 4)
. I.e., the running total is reinitialized to 0 for
each group.
Functions  

Function Details 
Combine inputs into a smaller number of outputs. If neither

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