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This extends `BUCKET` function to accept a two-parameters-only invocation: the first parameter remains as is, while the second is a span. It can be a numeric (floating point) span, if the first argument is numeric, or a date period or time duration, if the first argument is a date. Also, the function can now be invoked with the alias BIN. Additionally, the function has been turned into a grouping-only function and thus can only be used within a `STATS` command.
118 lines
3.3 KiB
Text
118 lines
3.3 KiB
Text
[discrete]
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[[esql-bucket]]
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=== `BUCKET`
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*Syntax*
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[source,esql]
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----
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BUCKET(expression, buckets, from, to)
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----
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*Parameters*
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`field`::
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Numeric or date expression from which to derive buckets.
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`buckets`::
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Target number of buckets.
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`from`::
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Start of the range. Can be a number or a date expressed as a string.
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`to`::
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End of the range. Can be a number or a date expressed as a string.
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*Description*
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Creates human-friendly buckets and returns a value for each row that corresponds
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to the resulting bucket the row falls into.
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Using a target number of buckets, a start of a range, and an end of a range,
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`BUCKET` picks an appropriate bucket size to generate the target number of
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buckets or fewer. For example, asking for at most 20 buckets over a year results
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in monthly buckets:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketMonth]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketMonth-result]
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|===
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The goal isn't to provide *exactly* the target number of buckets, it's to pick a
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range that people are comfortable with that provides at most the target number
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of buckets.
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Combine `BUCKET` with
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<<esql-stats-by>> to create a histogram:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketMonthlyHistogram]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketMonthlyHistogram-result]
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|===
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NOTE: `BUCKET` does not create buckets that don't match any documents.
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That's why this example is missing `1985-03-01` and other dates.
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Asking for more buckets can result in a smaller range. For example, asking for
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at most 100 buckets in a year results in weekly buckets:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketWeeklyHistogram]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketWeeklyHistogram-result]
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|===
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NOTE: `BUCKET` does not filter any rows. It only uses the provided range to
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pick a good bucket size. For rows with a value outside of the range, it returns
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a bucket value that corresponds to a bucket outside the range. Combine
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`BUCKET` with <<esql-where>> to filter rows.
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`BUCKET` can also operate on numeric fields. For example, to create a
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salary histogram:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketNumeric]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketNumeric-result]
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|===
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Unlike the earlier example that intentionally filters on a date range, you
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rarely want to filter on a numeric range. You have to find the `min` and `max`
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separately. {esql} doesn't yet have an easy way to do that automatically.
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*Examples*
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Create hourly buckets for the last 24 hours, and calculate the number of events
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per hour:
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[source.styled,esql]
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----
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include::{esql-specs}/bucket.csv-spec[tag=docsBucketLast24hr]
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----
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Create monthly buckets for the year 1985, and calculate the average salary by
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hiring month:
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[source.merge.styled,esql]
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----
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include::{esql-specs}/bucket.csv-spec[tag=bucket_in_agg]
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----
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[%header.monospaced.styled,format=dsv,separator=|]
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|===
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include::{esql-specs}/bucket.csv-spec[tag=bucket_in_agg-result]
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|===
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