gn3: genodb: Support reading columns.

* gn3/genodb.py (Matrix.__init__): Retrieve column pointers from database.
(row): Abstract out vector access code to ...
(Matrix.__vector): ... here.
(Matrix.column): New method.

1 files changed, 9 insertions, 3 deletions

diff --git a/gn3/genodb.py b/gn3/genodb.py
index 96bded6..c2decb8 100644
--- a/gn3/genodb.py
+++ b/gn3/genodb.py
@@ -24,10 +24,16 @@ class Matrix():
     def __init__(self, db, hash):
         self.nrows = int.from_bytes(db.get_metadata(hash, 'nrows'), byteorder='little')
         self.ncols = int.from_bytes(db.get_metadata(hash, 'ncols'), byteorder='little')
-        self.row_pointers = db.get(hash)
+        row_column_pointers = db.get(hash)
+        self.row_pointers = row_column_pointers[0 : self.nrows*db.hash_length]
+        self.column_pointers = row_column_pointers[self.nrows*db.hash_length :]
         self.db = db
-    def row(self, index):
+    def __vector(self, index, pointers):
         start = index * self.db.hash_length
         end = start + self.db.hash_length
-        return np.frombuffer(self.db.get(self.row_pointers[start:end]),
+        return np.frombuffer(self.db.get(pointers[start:end]),
                              dtype=np.uint8)
+    def row(self, index):
+        return self.__vector(index, self.row_pointers)
+    def column(self, index):
+        return self.__vector(index, self.column_pointers)