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avgMap

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Description

The Map combinator can be applied to the avg function to calculate the arithmetic mean of values in a Map according to each key, using the avgMap aggregate combinator function.

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Example usage

In this example, we’ll create a table that stores status codes and their counts for different timeslots, where each row contains a Map of status codes to their corresponding counts. We’ll use avgMap to calculate the average count for each status code within each timeslot.
Query
CREATE TABLE metrics(
    date Date,
    timeslot DateTime,
    status Map(String, UInt64)
) ENGINE = MergeTree
ORDER BY ();

INSERT INTO metrics VALUES
    ('2000-01-01', '2000-01-01 00:00:00', (['a', 'b', 'c'], [15, 25, 35])),
    ('2000-01-01', '2000-01-01 00:00:00', (['c', 'd', 'e'], [45, 55, 65])),
    ('2000-01-01', '2000-01-01 00:01:00', (['d', 'e', 'f'], [75, 85, 95])),
    ('2000-01-01', '2000-01-01 00:01:00', (['f', 'g', 'g'], [105, 115, 125]));

SELECT
    timeslot,
    avgMap(status),
FROM metrics
GROUP BY timeslot;
The avgMap function will calculate the average count for each status code within each timeslot. For example:
  • In timeslot ‘2000-01-01 00:00:00’:
    • Status ‘a’: 15
    • Status ‘b’: 25
    • Status ‘c’: (35 + 45) / 2 = 40
    • Status ‘d’: 55
    • Status ‘e’: 65
  • In timeslot ‘2000-01-01 00:01:00’:
    • Status ‘d’: 75
    • Status ‘e’: 85
    • Status ‘f’: (95 + 105) / 2 = 100
    • Status ‘g’: (115 + 125) / 2 = 120
Response
   ┌────────────timeslot─┬─avgMap(status)───────────────────────┐
1. │ 2000-01-01 00:01:00 │ {'d':75,'e':85,'f':100,'g':120}      │
2. │ 2000-01-01 00:00:00 │ {'a':15,'b':25,'c':40,'d':55,'e':65} │
   └─────────────────────┴──────────────────────────────────────┘

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See also