--- layout: doc_page --- # Transforming Dimension Values The following JSON fields can be used in a query to operate on dimension values. ## DimensionSpec `DimensionSpec`s define how dimension values get transformed prior to aggregation. ### Default DimensionSpec Returns dimension values as is and optionally renames the dimension. ```json { "type" : "default", "dimension" : , "outputName": } ``` ### Extraction DimensionSpec Returns dimension values transformed using the given [extraction function](#extraction-functions). ```json { "type" : "extraction", "dimension" : , "outputName" : , "extractionFn" : } ``` ## Extraction Functions Extraction functions define the transformation applied to each dimension value. Transformations can be applied to both regular (string) dimensions, as well as the special `__time` dimension, which represents the current time bucket according to the query [aggregation granularity](../querying/granularities.html). **Note**: for functions taking string values (such as regular expressions), `__time` dimension values will be formatted in [ISO-8601 format](https://en.wikipedia.org/wiki/ISO_8601) before getting passed to the extraction function. ### Regular Expression Extraction Function Returns the first matching group for the given regular expression. If there is no match, it returns the dimension value as is. ```json { "type" : "regex", "expr" : } ``` For example, using `"expr" : "(\\w\\w\\w).*"` will transform `'Monday'`, `'Tuesday'`, `'Wednesday'` into `'Mon'`, `'Tue'`, `'Wed'`. ### Partial Extraction Function Returns the dimension value unchanged if the regular expression matches, otherwise returns null. ```json { "type" : "partial", "expr" : } ``` ### Search Query Extraction Function Returns the dimension value unchanged if the given [`SearchQuerySpec`](../querying/searchqueryspec.html) matches, otherwise returns null. ```json { "type" : "searchQuery", "query" : } ``` ### Time Format Extraction Function Returns the dimension value formatted according to the given format string, time zone, and locale. For `__time` dimension values, this formats the time value bucketed by the [aggregation granularity](../querying/granularities.html) For a regular dimension, it assumes the string is formatted in [ISO-8601 date and time format](https://en.wikipedia.org/wiki/ISO_8601). * `format` : date time format for the resulting dimension value, in [Joda Time DateTimeFormat](http://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormat.html). * `locale` : locale (language and country) to use, given as a [IETF BCP 47 language tag](http://www.oracle.com/technetwork/java/javase/java8locales-2095355.html#util-text), e.g. `en-US`, `en-GB`, `fr-FR`, `fr-CA`, etc. * `timeZone` : time zone to use in [IANA tz database format](http://en.wikipedia.org/wiki/List_of_tz_database_time_zones), e.g. `Europe/Berlin` (this can possibly be different than the aggregation time-zone) ```json { "type" : "timeFormat", "format" : , "timeZone" : (optional), "locale" : (optional) } ``` For example, the following dimension spec returns the day of the week for Montréal in French: ```json { "type" : "extraction", "dimension" : "__time", "outputName" : "dayOfWeek", "extractionFn" : { "type" : "timeFormat", "format" : "EEEE", "timeZone" : "America/Montreal", "locale" : "fr" } } ``` ### Time Parsing Extraction Function Parses dimension values as timestamps using the given input format, and returns them formatted using the given output format. Note, if you are working with the `__time` dimension, you should consider using the [time extraction function instead](#time-format-extraction-function) instead, which works on time value directly as opposed to string values. Time formats are described in the [SimpleDateFormat documentation](http://icu-project.org/apiref/icu4j/com/ibm/icu/text/SimpleDateFormat.html) ```json { "type" : "time", "timeFormat" : , "resultFormat" : } ``` ### Javascript Extraction Function Returns the dimension value, as transformed by the given JavaScript function. For regular dimensions, the input value is passed as a string. For the `__time` dimension, the input value is passed as a number representing the number of milliseconds since January 1, 1970 UTC. Example for a regular dimension ```json { "type" : "javascript", "function" : "function(str) { return str.substr(0, 3); }" } ``` ```json { "type" : "javascript", "function" : "function(str) { return str + '!!!'; }", "injective" : true } ``` A property of `injective` specifies if the javascript function preserves uniqueness. The default value is `false` meaning uniqueness is not preserved Example for the `__time` dimension: ```json { "type" : "javascript", "function" : "function(t) { return 'Second ' + Math.floor((t % 60000) / 1000); }" } ``` ### Lookup extraction function Explicit lookups allow you to specify a set of keys and values to use when performing the extraction ```json { "type":"lookup", "lookup":{ "type":"map", "map":{"foo":"bar", "baz":"bat"} }, "retainMissingValue":true, "injective":true } ``` ```json { "type":"lookup", "lookup":{ "type":"map", "map":{"foo":"bar", "baz":"bat"} }, "retainMissingValue":false, "injective":false, "replaceMissingValueWith":"MISSING" } ``` ```json { "type":"lookup", "lookup":{"type":"namespace","namespace":"some_lookup"}, "replaceMissingValueWith":"Unknown", "injective":false } ``` ```json { "type":"lookup", "lookup":{"type":"namespace","namespace":"some_lookup"}, "retainMissingValue":true, "injective":false } ``` A lookup can be of type `namespace` or `map`. A `map` lookup is passed as part of the query. A `namespace` lookup is populated on all the nodes which handle queries as per [lookups](../querying/lookups.html) A property of `retainMissingValue` and `replaceMissingValueWith` can be specified at query time to hint how to handle missing values. Setting `replaceMissingValueWith` to `""` has the same effect of setting it to `null` or omitting the property. Setting `retainMissingValue` to true will use the dimension's original value if it is not found in the lookup. The default values are `replaceMissingValueWith = null` and `retainMissingValue = false` which causes missing values to be treated as missing. It is illegal to set `retainMissingValue = true` and also specify a `replaceMissingValueWith` A property of `injective` specifies if optimizations can be used which assume there is no combining of multiple names into one. For example: If ABC123 is the only key that maps to SomeCompany, that can be optimized since it is a unique lookup. But if both ABC123 and DEF456 BOTH map to SomeCompany, then that is NOT a unique lookup. Setting this value to true and setting `retainMissingValue` to FALSE (the default) may cause undesired behavior. A null dimension value can be mapped to a specific value by specifying the empty string as the key. This allows distinguishing between a null dimension and a lookup resulting in a null. For example, specifying `{"":"bar","bat":"baz"}` with dimension values `[null, "foo", "bat"]` and replacing missing values with `"oof"` will yield results of `["bar", "oof", "baz"]`. Omitting the empty string key will cause the missing value to take over. For example, specifying `{"bat":"baz"}` with dimension values `[null, "foo", "bat"]` and replacing missing values with `"oof"` will yield results of `["oof", "oof", "baz"]`.