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Extended faiss_to_nanopq() to convert faiss.IndexPreTransform (OPQMatrix+IndexPQ) #19

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49 changes: 36 additions & 13 deletions nanopq/convert_faiss.py
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@

import numpy as np

from .opq import OPQ
from .pq import PQ


Expand Down Expand Up @@ -48,29 +49,51 @@ def nanopq_to_faiss(pq_nanopq):


def faiss_to_nanopq(pq_faiss):
"""Convert a `faiss.IndexPQ <https://github.com/facebookresearch/faiss/blob/master/IndexPQ.h>`_ instance to :class:`nanopq.PQ`.
"""Convert a `faiss.IndexPQ <https://github.com/facebookresearch/faiss/blob/master/IndexPQ.h>`_
or a `faiss.IndexPreTransform <https://github.com/facebookresearch/faiss/blob/master/IndexPreTransform.h>`_ instance to :class:`nanopq.OPQ`.
To use this function, `faiss module needs to be installed <https://github.com/facebookresearch/faiss/blob/master/INSTALL.md>`_.

Args:
pq_faiss (faiss.IndexPQ): An input PQ instance.
pq_faiss (Union[faiss.IndexPQ, faiss.IndexPreTransform]): An input PQ or OPQ instance.

Returns:
tuple:
* nanopq.PQ: A converted PQ instance, with the same codewords to the input.
* Union[nanopq.PQ, nanopq.OPQ]: A converted PQ or OPQ instance, with the same codewords to the input.
* np.ndarray: Stored PQ codes in the input IndexPQ, with the shape=(N, M). This will be empty if codes are not stored

"""
assert isinstance(pq_faiss, faiss.IndexPQ), "Error. pq_faiss must be IndexPQ"
assert isinstance(
pq_faiss, (faiss.IndexPQ, faiss.IndexPreTransform)
), "Error. pq_faiss must be IndexPQ or IndexPreTransform"
assert pq_faiss.is_trained, "Error. pq_faiss must have been trained"

pq_nanopq = PQ(M=pq_faiss.pq.M, Ks=int(2 ** pq_faiss.pq.nbits))
pq_nanopq.Ds = int(pq_faiss.pq.d / pq_faiss.pq.M)

# Extract codewords from pq_IndexPQ.ProductQuantizer, reshape them to M*Ks*Ds
codewords = faiss.vector_to_array(pq_faiss.pq.centroids).reshape(
pq_nanopq.M, pq_nanopq.Ks, pq_nanopq.Ds
)

pq_nanopq.codewords = codewords
if isinstance(pq_faiss, faiss.IndexPreTransform):
opq_matrix: faiss.LinearTransform = faiss.downcast_VectorTransform(
pq_faiss.chain.at(0)
)
pq_faiss: faiss.IndexPQ = faiss.downcast_index(pq_faiss.index)
pq_nanopq = OPQ(M=pq_faiss.pq.M, Ks=int(2**pq_faiss.pq.nbits))
pq_nanopq.pq.Ds = int(pq_faiss.pq.d / pq_faiss.pq.M)

# Extract codewords from pq_IndexPQ.ProductQuantizer, reshape them to M*Ks*Ds
codewords = faiss.vector_to_array(pq_faiss.pq.centroids).reshape(
pq_nanopq.M, pq_nanopq.Ks, pq_nanopq.Ds
)

pq_nanopq.pq.codewords = codewords
pq_nanopq.R = (
faiss.vector_to_array(opq_matrix.A)
.reshape(opq_matrix.d_out, opq_matrix.d_in)
.transpose(1, 0)
)
else:
pq_nanopq = PQ(M=pq_faiss.pq.M, Ks=int(2**pq_faiss.pq.nbits))
pq_nanopq.Ds = int(pq_faiss.pq.d / pq_faiss.pq.M)

# Extract codewords from pq_IndexPQ.ProductQuantizer, reshape them to M*Ks*Ds
codewords = faiss.vector_to_array(pq_faiss.pq.centroids).reshape(
pq_nanopq.M, pq_nanopq.Ks, pq_nanopq.Ds
)
pq_nanopq.codewords = codewords

return pq_nanopq, faiss.vector_to_array(pq_faiss.codes).reshape(-1, pq_faiss.pq.M)
37 changes: 36 additions & 1 deletion tests/test_convert_faiss.py
Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,7 @@ def test_nanopq_to_faiss(self):

self.assertTrue(np.array_equal(ids1, ids2))

def test_faiss_to_nanopq(self):
def test_faiss_to_nanopq_pq(self):
D, M, Ks = 32, 4, 256
Nt, Nb, Nq = 2000, 10000, 100
nbits = int(np.log2(Ks))
Expand All @@ -70,6 +70,41 @@ def test_faiss_to_nanopq(self):
pq_faiss.add(x=Xb)

pq_nanopq, Cb_faiss = nanopq.faiss_to_nanopq(pq_faiss=pq_faiss)
self.assertIsInstance(pq_nanopq, nanopq.PQ)
self.assertEqual(pq_nanopq.codewords.shape, (M, Ks, int(D / M)))

# Encoded results should be same
Cb_nanopq = pq_nanopq.encode(vecs=Xb)
self.assertTrue(np.array_equal(Cb_nanopq, Cb_faiss))

# Search result should be same
topk = 100
_, ids1 = pq_faiss.search(x=Xq, k=topk)
ids2 = np.array(
[
np.argsort(pq_nanopq.dtable(query=xq).adist(codes=Cb_nanopq))[:topk]
for xq in Xq
]
)
self.assertTrue(np.array_equal(ids1, ids2))

def test_faiss_to_nanopq_opq(self):
D, M, Ks = 32, 4, 256
Nt, Nb, Nq = 2000, 10000, 100
nbits = int(np.log2(Ks))
assert nbits == 8
Xt = np.random.rand(Nt, D).astype(np.float32)
Xb = np.random.rand(Nb, D).astype(np.float32)
Xq = np.random.rand(Nq, D).astype(np.float32)

pq_faiss = faiss.IndexPQ(D, M, nbits)
opq_matrix = faiss.OPQMatrix(D, M=M)
pq_faiss = faiss.IndexPreTransform(opq_matrix, pq_faiss)
pq_faiss.train(x=Xt)
pq_faiss.add(x=Xb)

pq_nanopq, Cb_faiss = nanopq.faiss_to_nanopq(pq_faiss=pq_faiss)
self.assertIsInstance(pq_nanopq, nanopq.OPQ)
self.assertEqual(pq_nanopq.codewords.shape, (M, Ks, int(D / M)))

# Encoded results should be same
Expand Down