Coral8 – Randomly Sampling a Stream

The example below randomly samples an input stream and inserts samples into a named window for later processing. A variable named Dice is “rolled” each time a new row enters the input stream. A row is copied into the window if Dice = 1.

-- Variable for random number
CREATE VARIABLE INTEGER Dice;
CREATE VARIABLE INTEGER DiceSides = 6;
 
-- Input stream
CREATE INPUT STREAM StreamIn
SCHEMA (
    Val INTEGER
);
 
-- Each time a row enters the input stream,
-- roll the Dice
ON StreamIn
SET Dice =
    TO_INTEGER(RANDOM() * TO_FLOAT(DiceSides)) + 1;
 
-- Some data entering the input stream
ATTACH INPUT ADAPTER RMG
    TYPE RandomTuplesGeneratorAdapterType
TO STREAM StreamIn
PROPERTIES
    RATE     = "20"
    ,ROWCOUNT = "600"
;
 
-- Named window for samples
CREATE WINDOW WR
SCHEMA(
    Val INTEGER
    ,Dice INTEGER
)
KEEP 150 ROWS
;
 
-- Randomly sample the input stream
INSERT
    WHEN Dice = 1 THEN WR
SELECT Val, Dice
    FROM StreamIn
;

Here is a result, out of 600 messages that entered the input stream, 96 ended in the window; I was using a six-sided die — not bad.