[[slop]] === Mixing It Up

Requiring exact-phrase matches ((("proximity matching", "slop parameter")))may be too strict a constraint. Perhaps we do want documents that contain quick brown fox'' to be considered a match for the query quick fox,'' even though the positions aren't exactly equivalent.

We can introduce a degree ((("slop parameter")))of flexibility into phrase matching by using the slop parameter:

[source,js]

GET /my_index/my_type/_search { "query": { "match_phrase": { "title": { "query": "quick fox", "slop": 1 } } } }

---

// SENSE: 120_Proximity_Matching/10_Slop.json

The slop parameter tells the match_phrase query how((("match_phrase query", "slop parameter"))) far apart terms are allowed to be while still considering the document a match. By how far apart we mean how many times do you need to move a term in order to make the query and document match?

We'll start with a simple example. To make the query quick fox match a document containing quick brown fox we need a slop of just 1:

            Pos 1         Pos 2         Pos 3
-----------------------------------------------
Doc:        quick         brown         fox
-----------------------------------------------
Query:      quick         fox
Slop 1:     quick                 ↳     fox
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Although all words need to be present in phrase matching, even when using slop, the words don't necessarily need to be in the same sequence in order to match. With a high enough slop value, words can be arranged in any order.

To make the query fox quick match our document, we need a slop of 3:

            Pos 1         Pos 2         Pos 3
-----------------------------------------------
Doc:        quick         brown         fox
-----------------------------------------------
Query:      fox           quick
Slop 1:     fox|quick  ↵  <1>
Slop 2:     quick      ↳  fox
Slop 3:     quick                 ↳     fox
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<1> Note that fox and quick occupy the same position in this step. Switching word order from fox quick to quick fox thus requires two steps, or a slop of 2.