How does facets work

Volker · December 27, 2013, 5:41pm

Dear Readers

I have a question about facets and doing some filtering based on facets.

In the moment I am using hibernate search in combination with bobobrowse
for facetting and I am thinking about switching to ES. But before that I
would like to check whether I can still get the same functionality.

lets asume that I have an index about cars and some facets -- eg. model and
color.

color
[ ] red (10)
[ ] blue (5)
[ ] green (2)

model
[ ] bmw (4)
[ ] vw (5)
[ ] ford (8)

if I select a model I would like to get only color facets for that model,
but I still would like to get facets for all models. eg:

color
[ ] red (2)
[ ] blue (2)
[ ] green (1)

model
[ ] bmw (4)
[x] vw (5)
[ ] ford (8)

I have searched I did not find an example about this usecase. Is this
possible and if yes, how do I filter a query to get these results?

Kind regards

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Ivan · December 27, 2013, 5:58pm

Facets work on the documents returned by the query. This behavior will not
work in your case since you would like to gather facets on a greater set of
documents, not just the ones returned by the query. To solve this issue,
elasticsearch provides a post filter, which affects the result document
set, but not the set of documents that the facets work on.

The term "filter" is a bit overloaded in elasticsearch, so the team renamed
the post filter to a more explicit "post_filter":

github.com/elastic/elasticsearch

Rename filter param to search api "post_filter"

opened 04:27PM - 07 Nov 13 UTC

closed 04:10PM - 16 Dec 13 UTC

clintongormley

>enhancement v1.0.0.RC1 v0.90.8

Users tend to use the top-level `filter` param for general filtering, instead of… using a `filtered` query. It should be renamed to `post_filter` to dissuade users from using it unless they understand what it is for and `filter` should be deprecated. The top level `filter` is still valid field for backwards compatibility, but it will removed in the future.

The post filter documentation has some insight on how the filters affect
the facets. In your case, you want a filtered query (

)
with the color as the filter, but the model filter will be applied as a
post filter. Hopefully this makes sense.

Cheers,

Ivan

On Fri, Dec 27, 2013 at 9:41 AM, Volker svs@klest.de wrote:

Dear Readers

I have a question about facets and doing some filtering based on facets.

In the moment I am using hibernate search in combination with bobobrowse
for facetting and I am thinking about switching to ES. But before that I
would like to check whether I can still get the same functionality.

lets asume that I have an index about cars and some facets -- eg. model
and color.

color
red (10)
blue (5)
green (2)

model
bmw (4)
vw (5)
ford (8)

if I select a model I would like to get only color facets for that model,
but I still would like to get facets for all models. eg:

color
red (2)
blue (2)
green (1)

model
bmw (4)
vw (5)
ford (8)

I have searched I did not find an example about this usecase. Is this
possible and if yes, how do I filter a query to get these results?

Kind regards

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Volker · December 27, 2013, 6:24pm

Dear Ivan

thank you very much for your pointers. I will read through it and come
back, if I have further questions!

thanks

Am Freitag, 27. Dezember 2013 18:58:13 UTC+1 schrieb Ivan Brusic:

Facets work on the documents returned by the query. This behavior will
not work in your case since you would like to gather facets on a greater
set of documents, not just the ones returned by the query. To solve this
issue, elasticsearch provides a post filter, which affects the result
document set, but not the set of documents that the facets work on.

The term "filter" is a bit overloaded in elasticsearch, so the team
renamed the post filter to a more explicit "post_filter":

Elasticsearch Platform — Find real-time answers at scale | Elastic
Rename filter param to search api "post_filter" · Issue #4119 · elastic/elasticsearch · GitHub

The post filter documentation has some insight on how the filters affect
the facets. In your case, you want a filtered query (
Elasticsearch Platform — Find real-time answers at scale | Elastic )
with the color as the filter, but the model filter will be applied as a
post filter. Hopefully this makes sense.

Cheers,

Ivan

On Fri, Dec 27, 2013 at 9:41 AM, Volker <s...@klest.de <javascript:>>wrote:

Dear Readers

I have a question about facets and doing some filtering based on facets.

In the moment I am using hibernate search in combination with bobobrowse
for facetting and I am thinking about switching to ES. But before that I
would like to check whether I can still get the same functionality.

lets asume that I have an index about cars and some facets -- eg. model
and color.

color
red (10)
blue (5)
green (2)

model
bmw (4)
vw (5)
ford (8)

if I select a model I would like to get only color facets for that model,
but I still would like to get facets for all models. eg:

color
red (2)
blue (2)
green (1)

model
bmw (4)
vw (5)
ford (8)

I have searched I did not find an example about this usecase. Is this
possible and if yes, how do I filter a query to get these results?

Kind regards

--
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Volker · December 30, 2013, 3:57pm

Hopefully this makes sense.

after reading through your provided links... not totally

If I apply the selected facet before the the facet calculation, the facet
will count only elements, that are part of the result. That would mean,
that I would not get numbers for the not selected models (in this case no
numbers for bmw and ford).

If I apply the selected facet as a post_filter, I will get the correct
numbers for the unselected models, but the facets for the color does not
represent the numbers for the selected model, but for all models.

But probably I have not understood it, as it was meant.

Could you please elaborate further, how the query/filter for a selected
facet should be formulated? I have not found any example for this. If there
is one online, I would appreciate a link to that example.

Kind regards

Am Freitag, 27. Dezember 2013 18:58:13 UTC+1 schrieb Ivan Brusic:

Facets work on the documents returned by the query. This behavior will
not work in your case since you would like to gather facets on a greater
set of documents, not just the ones returned by the query. To solve this
issue, elasticsearch provides a post filter, which affects the result
document set, but not the set of documents that the facets work on.

The term "filter" is a bit overloaded in elasticsearch, so the team
renamed the post filter to a more explicit "post_filter":

Elasticsearch Platform — Find real-time answers at scale | Elastic
Rename filter param to search api "post_filter" · Issue #4119 · elastic/elasticsearch · GitHub

The post filter documentation has some insight on how the filters affect
the facets. In your case, you want a filtered query (
Elasticsearch Platform — Find real-time answers at scale | Elastic )
with the color as the filter, but the model filter will be applied as a
post filter. Hopefully this makes sense.

Cheers,

Ivan

On Fri, Dec 27, 2013 at 9:41 AM, Volker <s...@klest.de <javascript:>>wrote:

Dear Readers

I have a question about facets and doing some filtering based on facets.

In the moment I am using hibernate search in combination with bobobrowse
for facetting and I am thinking about switching to ES. But before that I
would like to check whether I can still get the same functionality.

lets asume that I have an index about cars and some facets -- eg. model
and color.

color
red (10)
blue (5)
green (2)

model
bmw (4)
vw (5)
ford (8)

if I select a model I would like to get only color facets for that model,
but I still would like to get facets for all models. eg:

color
red (2)
blue (2)
green (1)

model
bmw (4)
vw (5)
ford (8)

I have searched I did not find an example about this usecase. Is this
possible and if yes, how do I filter a query to get these results?

Kind regards

--
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Ivan · December 30, 2013, 5:36pm

After reading your scenario again, I have modified slightly my suggestion.
You would still need to use a post filter since the facets need to work on
set of documents that is greater than the set returned. You can apply the
same post filter as a facet filter on the facet you want to reduce. Here is
an example:

gist.github.com

https://gist.github.com/brusic/8185134

gistfile1.js

{
  "query": {
    "match_all": {}
  },
  "filter": {
    "term": {
      "model": "vw"
    }
  },
  "facets": {

This file has been truncated. show original

--
Ivan

On Mon, Dec 30, 2013 at 7:57 AM, Volker svs@klest.de wrote:

Hopefully this makes sense.

after reading through your provided links... not totally

If I apply the selected facet before the the facet calculation, the facet
will count only elements, that are part of the result. That would mean,
that I would not get numbers for the not selected models (in this case no
numbers for bmw and ford).

If I apply the selected facet as a post_filter, I will get the correct
numbers for the unselected models, but the facets for the color does not
represent the numbers for the selected model, but for all models.

But probably I have not understood it, as it was meant.

Could you please elaborate further, how the query/filter for a selected
facet should be formulated? I have not found any example for this. If there
is one online, I would appreciate a link to that example.

Kind regards

Am Freitag, 27. Dezember 2013 18:58:13 UTC+1 schrieb Ivan Brusic:

Facets work on the documents returned by the query. This behavior will
not work in your case since you would like to gather facets on a greater
set of documents, not just the ones returned by the query. To solve this
issue, elasticsearch provides a post filter, which affects the result
document set, but not the set of documents that the facets work on.

The term "filter" is a bit overloaded in elasticsearch, so the team
renamed the post filter to a more explicit "post_filter":

Elasticsearch Platform — Find real-time answers at scale | Elastic
reference/current/search-request-post-filter.html
Rename filter param to search api "post_filter" · Issue #4119 · elastic/elasticsearch · GitHub

The post filter documentation has some insight on how the filters affect
the facets. In your case, you want a filtered query (
Elasticsearch Platform — Find real-time answers at scale | Elastic
reference/current/query-dsl-filtered-query.html ) with the color as the
filter, but the model filter will be applied as a post filter. Hopefully
this makes sense.

Cheers,

Ivan

On Fri, Dec 27, 2013 at 9:41 AM, Volker s...@klest.de wrote:

Dear Readers

I have a question about facets and doing some filtering based on facets.

In the moment I am using hibernate search in combination with bobobrowse
for facetting and I am thinking about switching to ES. But before that I
would like to check whether I can still get the same functionality.

lets asume that I have an index about cars and some facets -- eg. model
and color.

color
red (10)
blue (5)
green (2)

model
bmw (4)
vw (5)
ford (8)

if I select a model I would like to get only color facets for that
model, but I still would like to get facets for all models. eg:

color
red (2)
blue (2)
green (1)

model
bmw (4)
vw (5)
ford (8)

I have searched I did not find an example about this usecase. Is this
possible and if yes, how do I filter a query to get these results?

Kind regards

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Volker · December 30, 2013, 5:55pm

Dear Ivan

thank you very much for your fast and helpful response. I will create some
demo data and play with your snippet.

I really appreciate your help!

btw... I think my scenario is a very standard scenario for working with
facets -- e.g. every online shop is working in this fashion with facets.

kind regards
Volker

Am Montag, 30. Dezember 2013 18:36:31 UTC+1 schrieb Ivan Brusic:

After reading your scenario again, I have modified slightly my suggestion.
You would still need to use a post filter since the facets need to work on
set of documents that is greater than the set returned. You can apply the
same post filter as a facet filter on the facet you want to reduce. Here is
an example:

facet filter example · GitHub

--
Ivan

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spinscale · January 1, 2014, 8:16pm

Hey

Small correction: When using the global flag, facets ignore the query. See

That might help in your case (though from my experience it is likely that
you will end up with a couple of facets, from which each has a different
facet filter. But your mileage may vary).

--Alex

On Fri, Dec 27, 2013 at 6:58 PM, Ivan Brusic ivan@brusic.com wrote:

Facets work on the documents returned by the query. This behavior will
not work in your case since you would like to gather facets on a greater
set of documents, not just the ones returned by the query. To solve this
issue, elasticsearch provides a post filter, which affects the result
document set, but not the set of documents that the facets work on.

The term "filter" is a bit overloaded in elasticsearch, so the team
renamed the post filter to a more explicit "post_filter":

Elasticsearch Platform — Find real-time answers at scale | Elastic
Rename filter param to search api "post_filter" · Issue #4119 · elastic/elasticsearch · GitHub

The post filter documentation has some insight on how the filters affect
the facets. In your case, you want a filtered query (
Elasticsearch Platform — Find real-time answers at scale | Elastic )
with the color as the filter, but the model filter will be applied as a
post filter. Hopefully this makes sense.

Cheers,

Ivan

On Fri, Dec 27, 2013 at 9:41 AM, Volker svs@klest.de wrote:

Dear Readers

I have a question about facets and doing some filtering based on facets.

In the moment I am using hibernate search in combination with bobobrowse
for facetting and I am thinking about switching to ES. But before that I
would like to check whether I can still get the same functionality.

lets asume that I have an index about cars and some facets -- eg. model
and color.

color
red (10)
blue (5)
green (2)

model
bmw (4)
vw (5)
ford (8)

if I select a model I would like to get only color facets for that model,
but I still would like to get facets for all models. eg:

color
red (2)
blue (2)
green (1)

model
bmw (4)
vw (5)
ford (8)

I have searched I did not find an example about this usecase. Is this
possible and if yes, how do I filter a query to get these results?

Kind regards

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