# What type to choose to index a field that has only few possible values (more than 'boolean' but less than 'short') **URL:** \ **Category:** Elasticsearch\ **Created:** [November 13, 2012, 2:32pm UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695 "2012-11-13T14:32:53Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Tux\_Racer](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/tux_racer/32/2545_2.png) [@Tux\_Racer](https://discuss.elastic.co/u/Tux_Racer)\ **Post date:** [November 13, 2012, 2:32pm UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695/1 "2012-11-13T14:32:53Z")
Hello List, I would like to index photo meta data an one of the field to index is the aperture. This is the 'f' number which is a number that typically only takes a predefined, the set of possible values is more or less: 1.4, 2, 2.8, 4, 5.6, .... , 32 (powers of square root of 2, i.e. sqrt(2)^N where N is (approx.) in {0..12}) 1. What would be the best type to use to store this kind of values? 'float'? or a mapping to 'short' or 'integer'? If a number type is chosen, what would be the optimal precision step to use? (assuming one wants to do range queries) If one has only 2^4=16 possible values for a given field, what is the effect of using a type that can store 2^16=65536 different values? Or is that more effective to chosen a mapping to (say) the first 16 letters of the alphabet and choose a type 'string'? 1. Also, another related question: what is the effect of using a boolean value on the index? In databases, it is often not a good idea to use an index on boolean se Re: Putting an INDEX on a boolean field? [http://archives.postgresql.org/pgsql-sql/2005-06/msg00215.php](http://archives.postgresql.org/pgsql-sql/2005-06/msg00215.php) In elasticesearch, is that better to use a index on boolean, or to do filtering on the client app? are there risk to get the index uselessly much larger? As you can see, this question is a bit more about indexing in general than about elasticsearch in particular but I ask here as I want to use elasticsearch 😉 Thanks in advance! TuXRaceR -- ---
**Author:** ![Chris\_Male](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/chris_male/32/2607_2.png) [@Chris\_Male](https://discuss.elastic.co/u/Chris_Male)\ **Post date:** [November 13, 2012, 10:44pm UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695/2 "2012-11-13T22:44:51Z")
Hi, On Wednesday, November 14, 2012 3:32:53 AM UTC+13, tuxracer69 wrote: > Hello List, > > I would like to index photo meta data an one of the field to index is the > aperture. This is the 'f' number which is a number that typically only > takes a predefined, the set of possible values is more or less: > 1.4, 2, 2.8, 4, 5.6, .... , 32 > (powers of square root of 2, i.e. sqrt(2)^N where N is (approx.) in > {0..12}) > > 1. What would be the best type to use to store this kind of values? > 'float'? or a mapping to 'short' or 'integer'? Given you're using decimal values, sounds like you should use float. > If a number type is chosen, what would be the optimal precision step to > use? (assuming one wants to do range queries) The ideal precisionStep for floats is 4, which happens to be the default value chosen by Elasticsearch. > If one has only 2^4=16 possible values for a given field, what is the > effect of using a type that can store 2^16=65536 different values? Inside a Lucene index (like that used by Elasticsearch) there isn't really typing, there is just terms much like you'd find at the back of an encyclopaedia so there won't be any effect. > Or is that more effective to chosen a mapping to (say) the first 16 > letters of the alphabet and choose a type 'string'? > > 1. Also, another related question: what is the effect of using a boolean > value on the index? In databases, it is often not a good idea to use an > index on boolean se > > Re: Putting an INDEX on a boolean field? > [PostgreSQL: Re: Putting an INDEX on a boolean field?](http://archives.postgresql.org/pgsql-sql/2005-06/msg00215.php) > > In elasticesearch, is that better to use a index on boolean, or to do > filtering on the client app? are there risk to get the index uselessly much > larger? It's absolutely fine to use boolean values in Elasticsearch. They are not treated any differently to other values and you shouldn't experience any problems. > As you can see, this question is a bit more about indexing in general than > about elasticsearch in particular but I ask here as I want to use > elasticsearch 😉 > > Thanks in advance! > TuXRaceR -- ---
**Author:** ![phill](https://avatars.discourse-cdn.com/v4/letter/p/779978/32.png) [@phill](https://discuss.elastic.co/u/phill)\ **Post date:** [November 13, 2012, 11:49pm UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695/3 "2012-11-13T23:49:05Z")
On 11/13/2012 2:44 PM, Chris Male wrote: > Hi, > > On Wednesday, November 14, 2012 3:32:53 AM UTC+13, tuxracer69 wrote: > > ``` > Hello List, > > I would like to index photo meta data an one of the field to index > is the aperture. This is the 'f' number which is a number that > typically only takes a predefined, the set of possible values is > more or less: > 1.4, 2, 2.8, 4, 5.6, .... , 32 > (powers of square root of 2, i.e. sqrt(2)^N where N is (approx.) > in {0..12}) > > 1) What would be the best type to use to store this kind of values? > 'float'? or a mapping to 'short' or 'integer'? > > ``` > > Given you're using decimal values, sounds like you should use float. Actually, given that the values are from a fixed set of possible values, I see no reason to use a float. > ``` > If a number type is chosen, what would be the optimal precision > step to use? (assuming one wants to do range queries) > > ``` > > The ideal precisionStep for floats is 4, which happens to be the > default value chosen by Elasticsearch. > > ``` > If one has only 2^4=16 possible values for a given field, what is > the effect of using a type that can store 2^16=65536 different values? > > ``` > > Inside a Lucene index (like that used by Elasticsearch) there isn't > really typing, there is just terms much like you'd find at the back of > an encyclopaedia so there won't be any effect. > > ``` > Or is that more effective to chosen a mapping to (say) the first > 16 letters of the alphabet and choose a type 'string'? > > ``` I would choose integers, because back in my client code somewhere I know I would have some a constant where I was storing the name of some constant meaning the value F/5.6, e.g. var F\_5\_6 = 3; or in some map that take 3 back to enumerated constant. Then range queries would be in terms of the integer indices representing the range of all possible F-numbers. -Paul -- ---
**Author:** ![Tux\_Racer](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/tux_racer/32/2545_2.png) [@Tux\_Racer](https://discuss.elastic.co/u/Tux_Racer)\ **Post date:** [November 14, 2012, 10:34am UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695/4 "2012-11-14T10:34:45Z")
On 11/13/2012 11:51 PM, P. Hill wrote: > > ``` > > I would like to index photo meta data an one of the field to index > > is the aperture. This is the 'f' number which is a number that > > typically only takes a predefined, the set of possible values is > > more or less: > > 1.4, 2, 2.8, 4, 5.6, .... , 32 > > (powers of square root of 2, i.e. sqrt(2)^N where N is (approx.) > > in {0..12}) > > > > ``` > > I would choose integers, because back in my client code somewhere I > know I would have some a constant where I was storing the name of some > constant meaning the value F/5.6, > e.g. var F\_5\_6 = 3; > or in some map that take 3 back to enumerated constant. > > Then range queries would be in terms of the integer indices > representing the range of all possible F-numbers. > > -Paul Thank you guys for your input, I will go with the int type and store the N number in the formula above rather than the F number as the N distribution will be more uniform, TuXRaceR -- ---
**Author:** ![phill](https://avatars.discourse-cdn.com/v4/letter/p/779978/32.png) [@phill](https://discuss.elastic.co/u/phill)\ **Post date:** [November 15, 2012, 1:06am UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695/5 "2012-11-15T01:06:29Z")
On 11/14/2012 2:34 AM, Tux raceR wrote: > Thank you guys for your input, I will go with the int type and store > the N number in the formula above rather than the F number as the N > distribution will be more uniform, > TuXRaceR If you are using Java on your ES client side you can even have enums that have methods. For example, a asFloat() method that gives you the appropriate value of F\_5\_6 to use in the equation you mentioned. Other possibilities include a method that would run the calculation for you using values defined with each enumeration. I've found enums that can convert themselves to other values to be very useful on occassion. -Paul -- ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 3:04am UTC](https://discuss.elastic.co/t/what-type-to-choose-to-index-a-field-that-has-only-few-possible-values-more-than-boolean-but-less-than-short/9695/6 "2017-07-06T03:04:12Z")