# Analyzer for generating keywords **URL:** \ **Category:** Elasticsearch\ **Created:** [November 8, 2012, 8:53am UTC](https://discuss.elastic.co/t/analyzer-for-generating-keywords/9625 "2012-11-08T08:53:54Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Anton](https://avatars.discourse-cdn.com/v4/letter/a/d9b06d/32.png) [@Anton](https://discuss.elastic.co/u/Anton)\ **Post date:** [November 8, 2012, 8:53am UTC](https://discuss.elastic.co/t/analyzer-for-generating-keywords/9625/1 "2012-11-08T08:53:54Z")
Hi all, I have a potentially stupid noob question about analyzers. Is it possible to create an analyzer to populate a specified field in all records automatically? Specifically, I want to create a field with keywords based on a text field in that same record. I want to be able to do a check on which keywords were generated for each record, to verify what the analyzer is doing. Or do analyzers only work on indexing, and the results can't be inspected directly? Also, when an analyzer is applied to an index, does this also apply to existing records, or do these records need to be reindexed? If so, how is the reindexing triggered? Thanks! -- ---
**Author:** ![simonw\_2](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/simonw_2/32/1130_2.png) [@simonw\_2](https://discuss.elastic.co/u/simonw_2)\ **Post date:** [November 8, 2012, 9:44am UTC](https://discuss.elastic.co/t/analyzer-for-generating-keywords/9625/2 "2012-11-08T09:44:45Z")
Hey Anton, On Thursday, November 8, 2012 9:53:54 AM UTC+1, Anton wrote: > Hi all, > > I have a potentially stupid noob question about analyzers. In general an analyzer is usually used per field and the analyzer is used at index and at query time. So if you index a document elasticsearch chooses an analyzer and passes your text through the analyzer. The created tokens are then used to build the inverted index ( [Inverted index - Wikipedia](http://en.wikipedia.org/wiki/Inverted_index)). At query time the same thing happens, we pass the text through the analyzer and build the query based on the created tokens. > Is it possible to create an analyzer to populate a specified field in all > records automatically? Specifically, I want to create a field with keywords > based on a text field in that same record. I want to be able to do a check > on which keywords were generated for each record, to verify what the > analyzer is doing. Or do analyzers only work on indexing, and the results > can't be inspected directly? I am not sure if I understand this question. Each field in ES can have its own index / query analyzer and you can configure which field uses which analyzer via the mapping API. ( [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/mapping/)) The analyzers can also be defined freely via a REST endpoint when you create the index ( [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/index-modules/analysis/)). > Also, when an analyzer is applied to an index, does this also apply to > existing records, or do these records need to be reindexed? If so, how is > the reindexing triggered? you can't change your analyzers once they have been configured otherwise we would need to entriely reindex and that is sometimes not possible ie. if we need the data from a 3rd party resource. you should configure your analysis ahead of time. Yet, if you want to get more insight into what happens when you pass a certain string to ES you can checkout the analyze API ( [Elasticsearch Platform — Find real-time answers at scale | Elastic](http://www.elasticsearch.org/guide/reference/api/admin-indices-analyze.html)) that basically applies an analyzer to text and returns you the result as a json response. simon > Thanks! -- ---
**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, 3:05am UTC](https://discuss.elastic.co/t/analyzer-for-generating-keywords/9625/3 "2017-07-06T03:05:28Z")