diff --git a/examples/query-database.rs b/examples/query-database.rs
index ce64870a9..edd311f16 100644
--- a/examples/query-database.rs
+++ b/examples/query-database.rs
@@ -115,7 +115,7 @@ fn main() -> Result<(), Box<Error>> {
                         };
 
                         print!("{}: ", name);
-                        let areas = create_highlight_areas(&text, &doc.matches, attr);
+                        let areas = create_highlight_areas(&text, doc.matches.as_matches(), attr);
                         display_highlights(&text, &areas)?;
                         println!();
                     }
@@ -124,7 +124,7 @@ fn main() -> Result<(), Box<Error>> {
             }
 
             let mut matching_attributes = HashSet::new();
-            for _match in doc.matches {
+            for _match in doc.matches.as_matches() {
                 let attr = SchemaAttr::new(_match.attribute.attribute());
                 let name = schema.attribute_name(attr);
                 matching_attributes.insert(name);
diff --git a/src/rank/criterion/exact.rs b/src/rank/criterion/exact.rs
index 041a6ae67..759bd951e 100644
--- a/src/rank/criterion/exact.rs
+++ b/src/rank/criterion/exact.rs
@@ -2,21 +2,20 @@ use std::cmp::Ordering;
 use std::ops::Deref;
 
 use rocksdb::DB;
-use group_by::GroupBy;
 
-use crate::rank::{match_query_index, Document};
+use crate::rank::{Document, Matches};
 use crate::rank::criterion::Criterion;
 use crate::database::DatabaseView;
 use crate::Match;
 
 #[inline]
-fn contains_exact(matches: &[Match]) -> bool {
+fn contains_exact(matches: &&[Match]) -> bool {
     matches.iter().any(|m| m.is_exact)
 }
 
 #[inline]
-fn number_exact_matches(matches: &[Match]) -> usize {
-    GroupBy::new(matches, match_query_index).map(contains_exact).count()
+fn number_exact_matches(matches: &Matches) -> usize {
+    matches.query_index_groups().filter(contains_exact).count()
 }
 
 #[derive(Debug, Clone, Copy)]
diff --git a/src/rank/criterion/number_of_words.rs b/src/rank/criterion/number_of_words.rs
index 855d997ba..23cf36a2c 100644
--- a/src/rank/criterion/number_of_words.rs
+++ b/src/rank/criterion/number_of_words.rs
@@ -2,16 +2,14 @@ use std::cmp::Ordering;
 use std::ops::Deref;
 
 use rocksdb::DB;
-use group_by::GroupBy;
 
-use crate::rank::{match_query_index, Document};
+use crate::rank::{Document, Matches};
 use crate::rank::criterion::Criterion;
 use crate::database::DatabaseView;
-use crate::Match;
 
 #[inline]
-fn number_of_query_words(matches: &[Match]) -> usize {
-    GroupBy::new(matches, match_query_index).count()
+fn number_of_query_words(matches: &Matches) -> usize {
+    matches.query_index_groups().count()
 }
 
 #[derive(Debug, Clone, Copy)]
diff --git a/src/rank/criterion/sum_of_typos.rs b/src/rank/criterion/sum_of_typos.rs
index 409c37cb4..400650ad2 100644
--- a/src/rank/criterion/sum_of_typos.rs
+++ b/src/rank/criterion/sum_of_typos.rs
@@ -3,21 +3,18 @@ use std::ops::Deref;
 
 use rocksdb::DB;
 
-use group_by::GroupBy;
-
-use crate::rank::{match_query_index, Document};
+use crate::rank::{Document, Matches};
 use crate::rank::criterion::Criterion;
 use crate::database::DatabaseView;
-use crate::Match;
 
 #[inline]
-fn sum_matches_typos(matches: &[Match]) -> i8 {
+fn sum_matches_typos(matches: &Matches) -> i8 {
     let mut sum_typos = 0;
     let mut number_words = 0;
 
     // note that GroupBy will never return an empty group
     // so we can do this assumption safely
-    for group in GroupBy::new(matches, match_query_index) {
+    for group in matches.query_index_groups() {
         sum_typos += unsafe { group.get_unchecked(0).distance } as i8;
         number_words += 1;
     }
@@ -44,7 +41,7 @@ where D: Deref<Target=DB>
 mod tests {
     use super::*;
 
-    use crate::{DocumentId, Attribute, WordArea};
+    use crate::{Match, DocumentId, Attribute, WordArea};
 
     // typing: "Geox CEO"
     //
@@ -69,10 +66,7 @@ mod tests {
                     word_area: WordArea::new_faillible(0, 6)
                 },
             ];
-            Document {
-                id: DocumentId(0),
-                matches: matches,
-            }
+            Document::from_unsorted_matches(DocumentId(0), matches)
         };
 
         let doc1 = {
@@ -92,10 +86,7 @@ mod tests {
                     word_area: WordArea::new_faillible(0, 6)
                 },
             ];
-            Document {
-                id: DocumentId(1),
-                matches: matches,
-            }
+            Document::from_unsorted_matches(DocumentId(1), matches)
         };
 
         let lhs = sum_matches_typos(&doc0.matches);
@@ -126,10 +117,7 @@ mod tests {
                     word_area: WordArea::new_faillible(0, 6)
                 },
             ];
-            Document {
-                id: DocumentId(0),
-                matches: matches,
-            }
+            Document::from_unsorted_matches(DocumentId(0), matches)
         };
 
         let doc1 = {
@@ -142,10 +130,7 @@ mod tests {
                     word_area: WordArea::new_faillible(0, 6)
                 },
             ];
-            Document {
-                id: DocumentId(1),
-                matches: matches,
-            }
+            Document::from_unsorted_matches(DocumentId(1), matches)
         };
 
         let lhs = sum_matches_typos(&doc0.matches);
@@ -176,10 +161,7 @@ mod tests {
                     word_area: WordArea::new_faillible(0, 6)
                 },
             ];
-            Document {
-                id: DocumentId(0),
-                matches: matches,
-            }
+            Document::from_unsorted_matches(DocumentId(0), matches)
         };
 
         let doc1 = {
@@ -192,10 +174,7 @@ mod tests {
                     word_area: WordArea::new_faillible(0, 6)
                 },
             ];
-            Document {
-                id: DocumentId(1),
-                matches: matches,
-            }
+            Document::from_unsorted_matches(DocumentId(1), matches)
         };
 
         let lhs = sum_matches_typos(&doc0.matches);
diff --git a/src/rank/criterion/sum_of_words_attribute.rs b/src/rank/criterion/sum_of_words_attribute.rs
index 718ae7447..aea21c35f 100644
--- a/src/rank/criterion/sum_of_words_attribute.rs
+++ b/src/rank/criterion/sum_of_words_attribute.rs
@@ -2,19 +2,17 @@ use std::cmp::Ordering;
 use std::ops::Deref;
 
 use rocksdb::DB;
-use group_by::GroupBy;
 
+use crate::rank::{Document, Matches};
 use crate::database::DatabaseView;
-use crate::rank::{match_query_index, Document};
 use crate::rank::criterion::Criterion;
-use crate::Match;
 
 #[inline]
-fn sum_matches_attributes(matches: &[Match]) -> u16 {
+fn sum_matches_attributes(matches: &Matches) -> usize {
     // note that GroupBy will never return an empty group
     // so we can do this assumption safely
-    GroupBy::new(matches, match_query_index).map(|group| unsafe {
-        group.get_unchecked(0).attribute.attribute()
+    matches.query_index_groups().map(|group| {
+        unsafe { group.get_unchecked(0).attribute.attribute() as usize }
     }).sum()
 }
 
diff --git a/src/rank/criterion/sum_of_words_position.rs b/src/rank/criterion/sum_of_words_position.rs
index d0ebaa74f..0b27184ba 100644
--- a/src/rank/criterion/sum_of_words_position.rs
+++ b/src/rank/criterion/sum_of_words_position.rs
@@ -2,19 +2,17 @@ use std::cmp::Ordering;
 use std::ops::Deref;
 
 use rocksdb::DB;
-use group_by::GroupBy;
 
-use crate::database::DatabaseView;
-use crate::rank::{match_query_index, Document};
+use crate::rank::{Document, Matches};
 use crate::rank::criterion::Criterion;
-use crate::Match;
+use crate::database::DatabaseView;
 
 #[inline]
-fn sum_matches_attribute_index(matches: &[Match]) -> u32 {
+fn sum_matches_attribute_index(matches: &Matches) -> usize {
     // note that GroupBy will never return an empty group
     // so we can do this assumption safely
-    GroupBy::new(matches, match_query_index).map(|group| unsafe {
-        group.get_unchecked(0).attribute.word_index()
+    matches.query_index_groups().map(|group| {
+        unsafe { group.get_unchecked(0).attribute.word_index() as usize }
     }).sum()
 }
 
diff --git a/src/rank/criterion/words_proximity.rs b/src/rank/criterion/words_proximity.rs
index fc80dfaec..7fe3102d3 100644
--- a/src/rank/criterion/words_proximity.rs
+++ b/src/rank/criterion/words_proximity.rs
@@ -2,9 +2,8 @@ use std::cmp::{self, Ordering};
 use std::ops::Deref;
 
 use rocksdb::DB;
-use group_by::GroupBy;
 
-use crate::rank::{match_query_index, Document};
+use crate::rank::{Document, Matches};
 use crate::rank::criterion::Criterion;
 use crate::database::DatabaseView;
 use crate::Match;
@@ -34,9 +33,9 @@ fn min_proximity(lhs: &[Match], rhs: &[Match]) -> u32 {
     min_prox
 }
 
-fn matches_proximity(matches: &[Match]) -> u32 {
+fn matches_proximity(matches: &Matches) -> u32 {
     let mut proximity = 0;
-    let mut iter = GroupBy::new(matches, match_query_index);
+    let mut iter = matches.query_index_groups();
 
     // iterate over groups by windows of size 2
     let mut last = iter.next();
@@ -91,7 +90,8 @@ mod tests {
         //   soup -> of = 8
         // + of -> the  = 1
         // + the -> day = 8 (not 1)
-        assert_eq!(matches_proximity(matches), 17);
+        let matches = Matches::from_unsorted(matches.to_vec());
+        assert_eq!(matches_proximity(&matches), 17);
     }
 
     #[test]
@@ -118,7 +118,8 @@ mod tests {
         //   soup -> of = 1
         // + of -> the  = 1
         // + the -> day = 1
-        assert_eq!(matches_proximity(matches), 3);
+        let matches = Matches::from_unsorted(matches.to_vec());
+        assert_eq!(matches_proximity(&matches), 3);
     }
 }
 
@@ -152,6 +153,8 @@ mod bench {
             matches.push(match_);
         }
 
+        let matches = Matches::from_unsorted(matches.to_vec());
+
         bench.iter(|| {
             let proximity = matches_proximity(&matches);
             test::black_box(move || proximity)
diff --git a/src/rank/mod.rs b/src/rank/mod.rs
index 4d1b6b1ea..91392cbee 100644
--- a/src/rank/mod.rs
+++ b/src/rank/mod.rs
@@ -2,6 +2,13 @@ pub mod criterion;
 mod query_builder;
 mod distinct_map;
 
+use std::iter::FusedIterator;
+use std::slice::Iter;
+use std::ops::Range;
+
+use sdset::SetBuf;
+use group_by::GroupBy;
+
 use crate::{Match, DocumentId};
 
 pub use self::query_builder::{FilterFunc, QueryBuilder, DistinctQueryBuilder};
@@ -14,20 +21,120 @@ fn match_query_index(a: &Match, b: &Match) -> bool {
 #[derive(Debug, Clone)]
 pub struct Document {
     pub id: DocumentId,
-    pub matches: Vec<Match>,
+    pub matches: Matches,
 }
 
 impl Document {
-    pub fn new(doc: DocumentId, match_: Match) -> Self {
-        unsafe { Self::from_sorted_matches(doc, vec![match_]) }
+    pub fn new(id: DocumentId, match_: Match) -> Self {
+        let matches = SetBuf::new_unchecked(vec![match_]);
+        Self::from_matches(id, matches)
     }
 
-    pub fn from_matches(doc: DocumentId, mut matches: Vec<Match>) -> Self {
-        matches.sort_unstable();
-        unsafe { Self::from_sorted_matches(doc, matches) }
+    pub fn from_matches(id: DocumentId, matches: SetBuf<Match>) -> Self {
+        let matches = Matches::new(matches);
+        Self { id, matches }
     }
 
-    pub unsafe fn from_sorted_matches(id: DocumentId, matches: Vec<Match>) -> Self {
+    pub fn from_unsorted_matches(id: DocumentId, matches: Vec<Match>) -> Self {
+        let matches = Matches::from_unsorted(matches);
         Self { id, matches }
     }
 }
+
+#[derive(Debug, Clone)]
+pub struct Matches {
+    matches: SetBuf<Match>,
+    slices: Vec<Range<usize>>,
+}
+
+impl Matches {
+    pub fn new(matches: SetBuf<Match>) -> Matches {
+        let mut last_end = 0;
+        let mut slices = Vec::new();
+
+        for group in GroupBy::new(&matches, match_query_index) {
+            let start = last_end;
+            let end = last_end + group.len();
+            slices.push(Range { start, end });
+            last_end = end;
+        }
+
+        Matches { matches, slices }
+    }
+
+    pub fn from_unsorted(mut matches: Vec<Match>) -> Matches {
+        matches.sort_unstable();
+        let matches = SetBuf::new_unchecked(matches);
+        Matches::new(matches)
+    }
+
+    pub fn query_index_groups(&self) -> QueryIndexGroups {
+        QueryIndexGroups {
+            matches: &self.matches,
+            slices: self.slices.iter(),
+        }
+    }
+
+    pub fn as_matches(&self) -> &[Match] {
+        &self.matches
+    }
+}
+
+pub struct QueryIndexGroups<'a, 'b> {
+    matches: &'a [Match],
+    slices: Iter<'b, Range<usize>>,
+}
+
+impl<'a> Iterator for QueryIndexGroups<'a, '_> {
+    type Item = &'a [Match];
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.slices.next().cloned().map(|range| {
+            unsafe { self.matches.get_unchecked(range) }
+        })
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.slices.size_hint()
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        self.slices.nth(n).cloned().map(|range| {
+            unsafe { self.matches.get_unchecked(range) }
+        })
+    }
+
+    #[inline]
+    fn last(self) -> Option<Self::Item> {
+        let (matches, slices) = (self.matches, self.slices);
+        slices.last().cloned().map(|range| {
+            unsafe { matches.get_unchecked(range) }
+        })
+    }
+}
+
+impl ExactSizeIterator for QueryIndexGroups<'_, '_> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.slices.len()
+    }
+}
+
+impl FusedIterator for QueryIndexGroups<'_, '_> { }
+
+impl DoubleEndedIterator for QueryIndexGroups<'_, '_> {
+    #[inline]
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.slices.next_back().cloned().map(|range| {
+            unsafe { self.matches.get_unchecked(range) }
+        })
+    }
+}
diff --git a/src/rank/query_builder.rs b/src/rank/query_builder.rs
index 4df983f8a..3ec49d83d 100644
--- a/src/rank/query_builder.rs
+++ b/src/rank/query_builder.rs
@@ -116,7 +116,7 @@ where D: Deref<Target=DB>,
             }
         }
 
-        matches.into_iter().map(|(id, matches)| Document::from_matches(id, matches)).collect()
+        matches.into_iter().map(|(i, m)| Document::from_unsorted_matches(i, m)).collect()
     }
 }