149 lines
6.0 KiB
Plaintext
149 lines
6.0 KiB
Plaintext
[[search-aggregations-bucket-datehistogram-aggregation]]
|
|
=== Date Histogram Aggregation
|
|
|
|
A multi-bucket aggregation similar to the <<search-aggregations-bucket-histogram-aggregation,histogram>> except it can
|
|
only be applied on date values. Since dates are represented in elasticsearch internally as long values, it is possible
|
|
to use the normal `histogram` on dates as well, though accuracy will be compromised. The reason for this is in the fact
|
|
that time based intervals are not fixed (think of leap years and on the number of days in a month). For this reason,
|
|
we need special support for time based data. From a functionality perspective, this histogram supports the same features
|
|
as the normal <<search-aggregations-bucket-histogram-aggregation,histogram>>. The main difference is that the interval can be specified by date/time expressions.
|
|
|
|
Requesting bucket intervals of a month.
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"aggs" : {
|
|
"articles_over_time" : {
|
|
"date_histogram" : {
|
|
"field" : "date",
|
|
"interval" : "month"
|
|
}
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
|
|
Available expressions for interval: `year`, `quarter`, `month`, `week`, `day`, `hour`, `minute`, `second`
|
|
|
|
|
|
Fractional values are allowed for seconds, minutes, hours, days and weeks. For example 1.5 hours:
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"aggs" : {
|
|
"articles_over_time" : {
|
|
"date_histogram" : {
|
|
"field" : "date",
|
|
"interval" : "1.5h"
|
|
}
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
|
|
See <<time-units>> for accepted abbreviations.
|
|
|
|
==== Time Zone
|
|
|
|
By default, times are stored as UTC milliseconds since the epoch. Thus, all computation and "bucketing" / "rounding" is
|
|
done on UTC. It is possible to provide a time zone value, which will cause all bucket
|
|
computations to take place in the specified zone. The time returned for each bucket/entry is milliseconds since the
|
|
epoch in UTC. The parameters is called `time_zone`. It accepts either a numeric value for the hours offset, for example:
|
|
`"time_zone" : -2`. It also accepts a format of hours and minutes, like `"time_zone" : "-02:30"`.
|
|
Another option is to provide a time zone accepted as one of the values listed here.
|
|
|
|
Lets take an example. For `2012-04-01T04:15:30Z` (UTC), with a `time_zone` of `"-08:00"`. For day interval, the actual time by
|
|
applying the time zone and rounding falls under `2012-03-31`, so the returned value will be (in millis) of
|
|
`2012-03-31T08:00:00Z` (UTC). For hour interval, internally applying the time zone results in `2012-03-31T20:15:30`, so rounding it
|
|
in the time zone results in `2012-03-31T20:00:00`, but we return that rounded value converted back in UTC so be consistent as
|
|
`2012-04-01T04:00:00Z` (UTC).
|
|
|
|
==== Offset
|
|
|
|
The `offset` option can be provided for shifting the date bucket intervals boundaries after any other shifts because of
|
|
time zones are applies. This for example makes it possible that daily buckets go from 6AM to 6AM the next day instead of starting at 12AM
|
|
or that monthly buckets go from the 10th of the month to the 10th of the next month instead of the 1st.
|
|
|
|
The `offset` option accepts positive or negative time durations like "1h" for an hour or "1M" for a Month. See <<time-units>> for more
|
|
possible time duration options.
|
|
|
|
==== Keys
|
|
|
|
Since internally, dates are represented as 64bit numbers, these numbers are returned as the bucket keys (each key
|
|
representing a date - milliseconds since the epoch). It is also possible to define a date format, which will result in
|
|
returning the dates as formatted strings next to the numeric key values:
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"aggs" : {
|
|
"articles_over_time" : {
|
|
"date_histogram" : {
|
|
"field" : "date",
|
|
"interval" : "1M",
|
|
"format" : "yyyy-MM-dd" <1>
|
|
}
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
|
|
<1> Supports expressive date <<date-format-pattern,format pattern>>
|
|
|
|
Response:
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"aggregations": {
|
|
"articles_over_time": {
|
|
"buckets": [
|
|
{
|
|
"key_as_string": "2013-02-02",
|
|
"key": 1328140800000,
|
|
"doc_count": 1
|
|
},
|
|
{
|
|
"key_as_string": "2013-03-02",
|
|
"key": 1330646400000,
|
|
"doc_count": 2
|
|
},
|
|
...
|
|
]
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
|
|
Like with the normal <<search-aggregations-bucket-histogram-aggregation,histogram>>, both document level scripts and
|
|
value level scripts are supported. It is also possible to control the order of the returned buckets using the `order`
|
|
settings and filter the returned buckets based on a `min_doc_count` setting (by default all buckets between the first
|
|
bucket that matches documents and the last one are returned). This histogram also supports the `extended_bounds`
|
|
setting, which enables extending the bounds of the histogram beyond the data itself (to read more on why you'd want to
|
|
do that please refer to the explanation <<search-aggregations-bucket-histogram-aggregation-extended-bounds,here>>).
|
|
|
|
==== Missing value
|
|
|
|
The `missing` parameter defines how documents that are missing a value should be treated.
|
|
By default they will be ignored but it is also possible to treat them as if they
|
|
had a value.
|
|
|
|
[source,js]
|
|
--------------------------------------------------
|
|
{
|
|
"aggs" : {
|
|
"publish_date" : {
|
|
"datehistogram" : {
|
|
"field" : "publish_date",
|
|
"interval": "year",
|
|
"missing": "2000-01-01" <1>
|
|
}
|
|
}
|
|
}
|
|
}
|
|
--------------------------------------------------
|
|
|
|
<1> Documents without a value in the `publish_date` field will fall into the same bucket as documents that have the value `2000-01-01`.
|