[[symbol-synonyms]] === Symbol Synonyms The final part of this chapter is devoted to symbol synonyms, which are unlike the synonyms((("symbol synonyms")))((("synonyms", "symbol"))) we have discussed until now. _Symbol synonyms_ are string aliases used to represent symbols that would otherwise be removed during tokenization. While most punctuation is seldom important for full-text search, character combinations like emoticons((("emoticons"))) may be very signficant, even changing the meaning of the the text. Compare these: [role="pagebreak-before"] * I am thrilled to be at work on Sunday. * I am thrilled to be at work on Sunday :( The `standard` tokenizer would simply strip out the emoticon in the second sentence, conflating two sentences that have quite different intent. We can use the http://bit.ly/1ziua5n[`mapping` character filter] to replace emoticons((("mapping character filter", "replacing emoticons with symbol synonyms")))((("emoticons", "replacing with symbol synonyms"))) with symbol synonyms like `emoticon_happy` and `emoticon_sad` before the text is passed to the tokenizer: [source,json] -------------------------------------- PUT /my_index { "settings": { "analysis": { "char_filter": { "emoticons": { "type": "mapping", "mappings": [ <1> ":)=>emoticon_happy", ":(=>emoticon_sad" ] } }, "analyzer": { "my_emoticons": { "char_filter": "emoticons", "tokenizer": "standard", "filter": [ "lowercase" ] ] } } } } } GET /my_index/_analyze?analyzer=my_emoticons I am :) not :( <2> -------------------------------------- <1> The `mappings` filter replaces the characters to the left of `=>` with those to the right. <2> Emits tokens `i`, `am`, `emoticon_happy`, `not`, `emoticon_sad`. It is unlikely that anybody would ever search for `emoticon_happy`, but ensuring that important symbols like emoticons are included in the index can be helpful when doing sentiment analysis. Of course, we could equally have used real words, like `happy` and `sad`. TIP: The `mapping` character filter is useful for simple replacements of exact character sequences. ((("mapping character filter", "replacements of exact character sequences")))For more-flexible pattern matching, you can use regular expressions with the http://bit.ly/1DK4hgy[`pattern_replace` character filter].