[[ml-count-functions]]
=== Count Functions

The {xpackml} features include the following count functions:

* `count`, `high_count`, `low_count`
* `non_zero_count`, `high_non_zero_count`, `low_non_zero_count`
* `distinct_count`, `high_distinct_count`, `low_distinct_count`

Count functions detect anomalies when the count of events in a bucket is
anomalous.

Use `non_zero_count` functions if your data is sparse and you want to ignore
cases where the bucket count is zero.

Use `distinct_count` functions to determine when the number of distinct values
in one field is unusual, as opposed to the total count.

Use high-sided functions if you want to monitor unusually high event rates.
Use low-sided functions if you want to look at drops in event rate.


////
* <<ml-count>>
* <<ml-high-count>>
* <<ml-low-count>>
* <<ml-nonzero-count>>
* <<ml-high-nonzero-count>>
* <<ml-low-nonzero-count>>

[float]
[[ml-count]]
===== Count

The `count` function detects anomalies when the count of events in a bucket is
anomalous.

* field_name: not applicable
* by_field_name: optional
* over_field_name: optional

[source,js]
--------------------------------------------------
{ "function" : "count" }
--------------------------------------------------

This example is probably the simplest possible analysis! It identifies time
buckets during which the overall count of events is higher or lower than usual.

It models the event rate and detects when the event rate is unusual compared to
the past.

[float]
[[ml-high-count]]
===== High_count

The `high_count` function detects anomalies when the count of events in a
bucket are unusually high.

* field_name: not applicable
* by_field_name: optional
* over_field_name: optional

[source,js]
--------------------------------------------------
{ "function" : "high_count", "byFieldName" : "error_code", "overFieldName": "user" }
--------------------------------------------------

This example models the event rate for each error code. It detects users that
generate an unusually high count of error codes compared to other users.

[float]
[[ml-low-count]]
===== Low_count

The `low_count` function detects anomalies when the count of events in a
bucket are unusually low.

* field_name: not applicable
* by_field_name: optional
* over_field_name: optional

[source,js]
--------------------------------------------------
{ "function" : "low_count", "byFieldName" : "status_code" }
--------------------------------------------------

In this example, there is a data stream that contains a field “status”. The
function detects when the count of events for a given status code is lower than
usual. It models the event rate for each status code and detects when a status
code has an unusually low count compared to its past behavior.

If the data stream consists of web server access log records, for example,
a drop in the count of events for a particular status code might be an indication
that something isn’t working correctly.

[float]
[[ml-nonzero-count]]
===== Non_zero_count

non_zero_count:: count, but zeros are treated as null and ignored

[float]
[[ml-high-nonzero-count]]
===== High_non_zero_count

high_non_zero_count::: count, but zeros are treated as null and ignored

[float]
[[ml-low-nonzero-count]]
===== Low_non_zero_count

low_non_zero_count::: count, but zeros are treated as null and ignored

[float]
[[ml-low-count]]
===== Low_count
distinct_count:: distinct count

[float]
[[ml-low-count]]
===== Low_count
high_distinct_count::: distinct count

[float]
[[ml-low-count]]
===== Low_count
low_distinct_count::: distinct count
////