Replace nnzs with row_lengths for clarity (#99)

* Replace `nnzs` with `row_lengths` for clarity

The term `nnzs` (i.e. number of non-zeros) comes from sparse tensor nomenclature, but sparse tensors are an implementation detail of the dataloaders, not a domain concept we should be propagating throughout our code base. Instead, let's call them `row_lengths` which make sense as part of a ragged tensor representation throughout Merlin.

* Autoupdate precommit package versions

* Apply auto-formatting to appease the linter

.pre-commit-config.yaml

@@ -5,30 +5,30 @@ repos:
     hooks:
       - id: absolufy-imports
   - repo: https://github.com/timothycrosley/isort
-    rev: 5.10.1
+    rev: 5.12.0
     hooks:
       - id: isort
         additional_dependencies: [toml]
         exclude: examples/.*
   # code style
   - repo: https://github.com/python/black
-    rev: 22.6.0
+    rev: 23.1.0
     hooks:
       - id: black
   - repo: https://github.com/pycqa/pylint
-    rev: v2.14.1
+    rev: v2.16.1
     hooks:
       - id: pylint
   - repo: https://github.com/pycqa/flake8
-    rev: 3.9.2
+    rev: 6.0.0
     hooks:
       - id: flake8
   - repo: https://github.com/adrienverge/yamllint
-    rev: v1.28.0
+    rev: v1.29.0
     hooks:
       - id: yamllint
   - repo: https://github.com/pre-commit/mirrors-prettier
-    rev: v2.7.1
+    rev: v3.0.0-alpha.4
     hooks:
       - id: prettier
         types_or: [yaml, markdown]
@@ -46,7 +46,7 @@ repos:
         exclude: ^(docs|examples|tests|setup.py|versioneer.py)
         args: [--config=pyproject.toml]
   - repo: https://github.com/codespell-project/codespell
-    rev: v2.2.1
+    rev: v2.2.2
     hooks:
       - id: codespell
         exclude: .github/.*

merlin/dataloader/loader_base.py

@@ -51,7 +51,7 @@ def _num_steps(num_samples, step_size):
 class LoaderBase:
     """Base class containing common functionality between the PyTorch and TensorFlow dataloaders."""
 
-    _use_nnz = False
+    _use_row_lengths = False
 
     def __init__(
         self,
@@ -337,15 +337,15 @@ def _get_next_batch(self):
         return batch
 
     @annotate("make_tensors", color="darkgreen", domain="merlin_dataloader")
-    def make_tensors(self, gdf, use_nnz=False):
+    def make_tensors(self, gdf, use_row_lengths=False):
         """Turns a gdf into tensor representation by column
 
         Parameters
         ----------
         gdf : DataFrame
             A dataframe type object.
-        use_nnz : bool, optional
-            toggle nnzs or use offsets for list columns, by default False
+        use_row_lengths : bool, optional
+            Enable using row lengths instead of offsets for list columns, by default False
 
         Returns
         -------
@@ -357,7 +357,7 @@ def make_tensors(self, gdf, use_nnz=False):
         # map from big chunk to framework-specific tensors
         chunks, names = self._create_tensors(gdf)
 
-        # if we have any offsets, calculate nnzs up front
+        # if we have any offsets, calculate row lengths up front
         # will need to get offsets if list columns detected in schema
 
         # if len(chunks) == 4:
@@ -368,8 +368,8 @@ def make_tensors(self, gdf, use_nnz=False):
         ]
         if len(lists_list) > 0:
             offsets = chunks[-1]
-            if use_nnz:
-                nnzs = offsets[1:] - offsets[:-1]
+            if use_row_lengths:
+                row_lengths = offsets[1:] - offsets[:-1]
             chunks = chunks[:-1]
 
         # split them into batches and map to the framework-specific output format
@@ -388,43 +388,43 @@ def make_tensors(self, gdf, use_nnz=False):
             if lists is not None:
                 num_list_columns = len(lists)
 
-                # grab the set of offsets and nnzs corresponding to
-                # the list columns from this chunk
+                # grab the set of offsets and row lengths
+                # corresponding to the list columns from this chunk
                 chunk_offsets = offsets[:, offset_idx : offset_idx + num_list_columns]
-                if use_nnz:
-                    chunk_nnzs = nnzs[:, offset_idx : offset_idx + num_list_columns]
+                if use_row_lengths:
+                    chunk_row_lengths = row_lengths[:, offset_idx : offset_idx + num_list_columns]
                 offset_idx += num_list_columns
 
                 # split them into batches, including an extra 1 on the offsets
                 # so we know how long the very last element is
                 batch_offsets = self._split_fn(chunk_offsets, split_idx + [1])
-                if use_nnz and len(split_idx) > 1:
-                    batch_nnzs = self._split_fn(chunk_nnzs, split_idx)
-                elif use_nnz:
-                    batch_nnzs = [chunk_nnzs]
+                if use_row_lengths and len(split_idx) > 1:
+                    batch_row_lengths = self._split_fn(chunk_row_lengths, split_idx)
+                elif use_row_lengths:
+                    batch_row_lengths = [chunk_row_lengths]
                 else:
-                    batch_nnzs = [None] * (len(batch_offsets) - 1)
+                    batch_row_lengths = [None] * (len(batch_offsets) - 1)
 
                 # group all these indices together and iterate through
                 # them in batches to grab the proper elements from each
                 # values tensor
-                chunk = zip(chunk, batch_offsets[:-1], batch_offsets[1:], batch_nnzs)
+                chunk = zip(chunk, batch_offsets[:-1], batch_offsets[1:], batch_row_lengths)
 
             for n, c in enumerate(chunk):
                 if isinstance(c, tuple):
-                    c, off0s, off1s, _nnzs = c
+                    c, off0s, off1s, _row_lengths = c
                     offsets_split_idx = [1 for _ in range(num_list_columns)]
                     off0s = self._split_fn(off0s, offsets_split_idx, axis=1)
                     off1s = self._split_fn(off1s, offsets_split_idx, axis=1)
-                    if use_nnz:
-                        _nnzs = self._split_fn(_nnzs, offsets_split_idx, axis=1)
+                    if use_row_lengths:
+                        _row_lengths = self._split_fn(_row_lengths, offsets_split_idx, axis=1)
 
                     # TODO: does this need to be ordereddict?
                     batch_lists = {}
                     for k, (column_name, values) in enumerate(lists.items()):
                         off0, off1 = off0s[k], off1s[k]
-                        if use_nnz:
-                            nnz = _nnzs[k]
+                        if use_row_lengths:
+                            row_length = _row_lengths[k]
 
                         # need to grab scalars for TF case
                         if len(off0.shape) == 1:
@@ -435,7 +435,7 @@ def make_tensors(self, gdf, use_nnz=False):
                             print(off0, off1)
                             raise ValueError
                         value = values[int(start) : int(stop)]
-                        index = off0 - start if not use_nnz else nnz
+                        index = off0 - start if not use_row_lengths else row_length
                         batch_lists[column_name] = (value, index)
                     c = (c, batch_lists)
 
@@ -829,7 +829,7 @@ def chunk_logic(self, itr):
                 chunks = shuffle_df(chunks)
 
             if len(chunks) > 0:
-                chunks = self.dataloader.make_tensors(chunks, self.dataloader._use_nnz)
+                chunks = self.dataloader.make_tensors(chunks, self.dataloader._use_row_lengths)
                 # put returns True if buffer is stopped before
                 # packet can be put in queue. Keeps us from
                 # freezing on a put on a full queue
@@ -838,7 +838,7 @@ def chunk_logic(self, itr):
             chunks = None
         # takes care final batch, which is less than batch size
         if not self.dataloader.drop_last and spill is not None and not spill.empty:
-            spill = self.dataloader.make_tensors(spill, self.dataloader._use_nnz)
+            spill = self.dataloader.make_tensors(spill, self.dataloader._use_row_lengths)
             self.put(spill)
 
     @annotate("load_chunks", color="darkgreen", domain="merlin_dataloader")

merlin/dataloader/tensorflow.py

@@ -102,7 +102,7 @@ class Loader(tf.keras.utils.Sequence, LoaderBase):
         will usually contain fewer rows.
     """
 
-    _use_nnz = True
+    _use_row_lengths = True
 
     def __init__(
         self,

merlin/dataloader/utils/tf/tf_trainer.py

@@ -90,7 +90,7 @@ def seed_fn():
 for col in CATEGORICAL_MH_COLUMNS:
     inputs[col] = (
         tf.keras.Input(name=f"{col}__values", dtype=tf.int64, shape=(1,)),
-        tf.keras.Input(name=f"{col}__nnzs", dtype=tf.int64, shape=(1,)),
+        tf.keras.Input(name=f"{col}__lengths", dtype=tf.int64, shape=(1,)),
     )
 for col in CATEGORICAL_COLUMNS + CATEGORICAL_MH_COLUMNS:
     emb_layers.append(

tests/unit/dataloader/test_tf_dataloader.py

@@ -382,7 +382,7 @@ def test_mh_support(tmpdir, multihot_data, multihot_dataset, batch_size):
         batch_size=batch_size,
         shuffle=False,
     )
-    nnzs = None
+    row_lengths = None
     idx = 0
 
     for X, y in data_itr:
@@ -391,18 +391,18 @@ def test_mh_support(tmpdir, multihot_data, multihot_dataset, batch_size):
 
         for mh_name in ["Authors", "Reviewers", "Embedding"]:
             # assert (mh_name) in X
-            array, nnzs = X[mh_name]
-            nnzs = nnzs.numpy()[:, 0]
+            array, row_lengths = X[mh_name]
+            row_lengths = row_lengths.numpy()[:, 0]
             array = array.numpy()[:, 0]
 
             if mh_name == "Embedding":
-                assert (nnzs == 3).all()
+                assert (row_lengths == 3).all()
             else:
                 lens = [
                     len(x)
                     for x in multihot_data[mh_name][idx * batch_size : idx * batch_size + n_samples]
                 ]
-                assert (nnzs == np.array(lens)).all()
+                assert (row_lengths == np.array(lens)).all()
 
             if mh_name == "Embedding":
                 assert len(array) == (n_samples * 3)
@@ -533,7 +533,7 @@ def test_sparse_tensors(tmpdir, sparse_dense):
     for batch in data_itr:
         feats, labs = batch
         for col in spa_lst:
-            # grab nnzs
+            # grab row lengths
             feature_tensor = feats[f"{col}"]
             if not sparse_dense:
                 assert list(feature_tensor.shape) == [batch_size, spa_mx[col]]
@@ -648,7 +648,6 @@ def test_dataloader_schema(tmpdir, dataset, batch_size, cpu):
         batch_size=batch_size,
         shuffle=False,
     ) as data_loader:
-
         batch = data_loader.peek()
 
     columns = set(dataset.schema.column_names) - {"label"}