Home  Trees  Indices  Help 



red r [BINARY_FUNCTION ...]
Aggregates (reduces) objects from the input stream in a simpler but
less general way than the agg
command.
A BINARY_FUNCTION
takes two inputs and produces one
output. Binary operators and userdefined functions can be used as
BINARY_FUNCTION
s. Given a sequence of inputs such as
(1,), (2,), (3,)
, red
can be used to find the
sum:
... ^ red +
yields (6,)
. If each input sequence contains multiple
values, then multiple BINARY_FUNCTION
s can be provided. For
example, to find the sums of the first 10 integers, the sum of their
squares, and the sum of their cubes:
osh gen 10 ^ f 'x: (x, x**2, x**3)' ^ red + + + $
which yields the output (45, 285, 2025)
.
If .
is provided as one of the
BINARY_FUNCTION
s, then that value is not aggregated.
Instead, aggregation is done for the groups defined by the indicated
elements. For example, suppose the input sequence is:
(1, 10, 5, 100) (1, 10, 6, 200) (1, 11, 4, 100) (1, 11, 3, 200) (2, 20, 8, 100) (2, 20, 9, 200) (2, 20, 10, 300) (3, 30, 5, 100)
If this sequence is piped to this invocation of red
:
red . . + +
Then the output sequence would be:
(1, 10, 11, 300) (1, 11, 7, 300) (2, 20, 17, 300) (3, 30, 5, 100)
The two .
s, in the first two positions, mean that the
groups used for aggregation are (1, 10)
, (1,
11)
, (2, 20)
, and (3, 30)
. The (1,
10)
group has two rows, (1, 10, 5, 100)
, and
(1, 10, 6, 200)
. The two +
s mean that the items
in the last two fields should be summed. Adding the items in the third
position, 5 + 6 = 11; and in the last position, 100 + 200 = 300.
If the r
flag is specified, then one output object is
generated for each input object; the output object contains the current
accumulated values. 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:
... ^ red r + ^ ...
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:
... ^ red 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)
.
Functions  

Function Details 

Home  Trees  Indices  Help 


Generated by Epydoc 3.0.1 on Sun Oct 3 15:23:48 2010  http://epydoc.sourceforge.net 