Requiring exact-phrase matches 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 of flexibility into phrase matching by using the
slop parameter:
GET /my_index/my_type/_search
{
"query": {
"match_phrase": {
"title": {
"query": "quick fox",
"slop": 1
}
}
}
}The slop parameter tells the match_phrase query how 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
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
-
Note that
foxandquickoccupy the same position in this step. Switching word order fromfox quicktoquick foxthus requires two steps, or aslopof2.