1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
|
[[search-aggregations-bucket-histogram-aggregation]]
=== Histogram
A multi-bucket values source based aggregation that can be applied on numeric values extracted from the documents.
It dynamically builds fixed size (a.k.a. interval) buckets over the values. For example, if the documents have a field
that holds a price (numeric), we can configure this aggregation to dynamically build buckets with interval `5`
(in case of price it may represent $5). When the aggregation executes, the price field of every document will be
evaluated and will be rounded down to its closest bucket - for example, if the price is `32` and the bucket size is `5`
then the rounding will yield `30` and thus the document will "fall" into the bucket that is associated withe the key `30`.
To make this more formal, here is the rounding function that is used:
[source,java]
--------------------------------------------------
rem = value % interval
if (rem < 0) {
rem += interval
}
bucket_key = value - rem
--------------------------------------------------
The following snippet "buckets" the products based on their `price` by interval of `50`:
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50
}
}
}
}
--------------------------------------------------
And the following may be the response:
[source,js]
--------------------------------------------------
{
"aggregations": {
"prices" : {
"buckets": [
{
"key": 0,
"doc_count": 2
},
{
"key": 50,
"doc_count": 4
},
{
"key": 150,
"doc_count": 3
}
]
}
}
}
--------------------------------------------------
The response above shows that none of the aggregated products has a price that falls within the range of `[100 - 150)`.
By default, the response will only contain those buckets with a `doc_count` greater than 0. It is possible change that
and request buckets with either a higher minimum count or even 0 (in which case elasticsearch will "fill in the gaps"
and create buckets with zero documents). This can be configured using the `min_doc_count` setting:
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50,
"min_doc_count" : 0
}
}
}
}
--------------------------------------------------
Response:
[source,js]
--------------------------------------------------
{
"aggregations": {
"prices" : {
"buckets": [
{
"key": 0,
"doc_count": 2
},
{
"key": 50,
"doc_count": 4
},
{
"key" : 100,
"doc_count" : 0 <1>
},
{
"key": 150,
"doc_count": 3
}
]
}
}
}
--------------------------------------------------
<1> No documents were found that belong in this bucket, yet it is still returned with zero `doc_count`.
==== Order
By default the returned buckets are sorted by their `key` ascending, though the order behaviour can be controled
using the `order` setting.
Ordering the buckets by their key - descending:
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50,
"order" : { "_key" : "desc" }
}
}
}
}
--------------------------------------------------
Ordering the buckets by their `doc_count` - ascending:
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50,
"order" : { "_count" : "asc" }
}
}
}
}
--------------------------------------------------
If the histogram aggregation has a direct metrics sub-aggregation, the latter can determine the order of the buckets:
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50,
"order" : { "price_stats.min" : "asc" } <1>
},
"aggs" : {
"price_stats" : { "stats" : {} } <2>
}
}
}
}
--------------------------------------------------
<1> The `{ "price_stats.min" : asc" }` will sort the buckets based on `min` value of their their `price_stats` sub-aggregation.
<2> There is no need to configure the `price` field for the `price_stats` aggregation as it will inherit it by default from its parent histogram aggregation.
==== Minimum document count
It is possible to only return buckets that have a document count that is greater than or equal to a configured
limit through the `min_doc_count` option.
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50,
"min_doc_count": 10
}
}
}
}
--------------------------------------------------
The above aggregation would only return buckets that contain 10 documents or more. Default value is `1`.
NOTE: The special value `0` can be used to add empty buckets to the response between the minimum and the maximum buckets.
Here is an example of what the response could look like:
[source,js]
--------------------------------------------------
{
"aggregations": {
"prices": {
"buckets": {
"0": {
"key": 0,
"doc_count": 2
},
"50": {
"key": 50,
"doc_count": 0
},
"150": {
"key": 150,
"doc_count": 3
},
"200": {
"key": 150,
"doc_count": 0
},
"250": {
"key": 150,
"doc_count": 0
},
"300": {
"key": 150,
"doc_count": 1
}
}
}
}
}
--------------------------------------------------
==== Response Format
By default, the buckets are returned as an ordered array. It is also possible to request the response as a hash
instead keyed by the buckets keys:
[source,js]
--------------------------------------------------
{
"aggs" : {
"prices" : {
"histogram" : {
"field" : "price",
"interval" : 50,
"keyed" : true
}
}
}
}
--------------------------------------------------
Response:
[source,js]
--------------------------------------------------
{
"aggregations": {
"prices": {
"buckets": {
"0": {
"key": 0,
"doc_count": 2
},
"50": {
"key": 50,
"doc_count": 4
},
"150": {
"key": 150,
"doc_count": 3
}
}
}
}
}
--------------------------------------------------
|
