diff --git a/meilidb-data/Cargo.toml b/meilidb-data/Cargo.toml
index 18881367b..23749631b 100644
--- a/meilidb-data/Cargo.toml
+++ b/meilidb-data/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 
 [dependencies]
 bincode = "1.1.2"
+hashbrown = { version = "0.1.8", features = ["serde"] }
 linked-hash-map = { version = "0.5.2", features = ["serde_impl"] }
 meilidb-core = { path = "../meilidb-core", version = "0.1.0" }
 ordered-float = { version = "1.0.2", features = ["serde"] }
diff --git a/meilidb-data/src/ranked_map.rs b/meilidb-data/src/ranked_map.rs
new file mode 100644
index 000000000..7b4ff3735
--- /dev/null
+++ b/meilidb-data/src/ranked_map.rs
@@ -0,0 +1,5 @@
+use hashbrown::HashMap;
+use meilidb_core::DocumentId;
+use crate::{SchemaAttr, Number};
+
+pub type RankedMap = HashMap<(DocumentId, SchemaAttr), Number>;
diff --git a/meilidb/src/sort_by_attr.rs b/meilidb/src/sort_by_attr.rs
index b7a1013fd..f4c4bcc41 100644
--- a/meilidb/src/sort_by_attr.rs
+++ b/meilidb/src/sort_by_attr.rs
@@ -4,9 +4,7 @@ use std::fmt;
 
 use meilidb_core::criterion::Criterion;
 use meilidb_core::RawDocument;
-
-use meilidb_data::{Schema, SchemaAttr};
-use meilidb_data::RankedMap;
+use meilidb_data::{Schema, SchemaAttr, RankedMap};
 
 /// An helper struct that permit to sort documents by
 /// some of their stored attributes.