Add in user example that compares a two different approaches to UDFs (#770)

* Add in user example that compares a two different approaches to UDFs

* add license

Author: timsaucer

examples/python-udf-comparisons.py

@@ -0,0 +1,186 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+from datafusion import SessionContext, col, lit, udf, functions as F
+import os
+import pyarrow as pa
+import pyarrow.compute as pc
+import time
+
+path = os.path.dirname(os.path.abspath(__file__))
+filepath = os.path.join(path, "../tpch/data/lineitem.parquet")
+
+# This example serves to demonstrate alternate approaches to answering the
+# question "return all of the rows that have a specific combination of these
+# values". We have the combinations we care about provided as a python
+# list of tuples. There is no built in function that supports this operation,
+# but it can be explicilty specified via a single expression or we can
+# use a user defined function.
+
+ctx = SessionContext()
+
+# These part keys and suppliers are chosen because there are
+# cases where two suppliers each have two of the part keys
+# but we are interested in these specific combinations.
+
+values_of_interest = [
+    (1530, 4031, "N"),
+    (6530, 1531, "N"),
+    (5618, 619, "N"),
+    (8118, 8119, "N"),
+]
+
+partkeys = [lit(r[0]) for r in values_of_interest]
+suppkeys = [lit(r[1]) for r in values_of_interest]
+returnflags = [lit(r[2]) for r in values_of_interest]
+
+df_lineitem = ctx.read_parquet(filepath).select(
+    "l_partkey", "l_suppkey", "l_returnflag"
+)
+
+start_time = time.time()
+
+df_simple_filter = df_lineitem.filter(
+    F.in_list(col("l_partkey"), partkeys),
+    F.in_list(col("l_suppkey"), suppkeys),
+    F.in_list(col("l_returnflag"), returnflags),
+)
+
+num_rows = df_simple_filter.count()
+print(
+    f"Simple filtering has number {num_rows} rows and took {time.time() - start_time} s"
+)
+print("This is the incorrect number of rows!")
+start_time = time.time()
+
+# Explicitly check for the combinations of interest.
+# This works but is not scalable.
+
+filter_expr = (
+    (
+        (col("l_partkey") == values_of_interest[0][0])
+        & (col("l_suppkey") == values_of_interest[0][1])
+        & (col("l_returnflag") == values_of_interest[0][2])
+    )
+    | (
+        (col("l_partkey") == values_of_interest[1][0])
+        & (col("l_suppkey") == values_of_interest[1][1])
+        & (col("l_returnflag") == values_of_interest[1][2])
+    )
+    | (
+        (col("l_partkey") == values_of_interest[2][0])
+        & (col("l_suppkey") == values_of_interest[2][1])
+        & (col("l_returnflag") == values_of_interest[2][2])
+    )
+    | (
+        (col("l_partkey") == values_of_interest[3][0])
+        & (col("l_suppkey") == values_of_interest[3][1])
+        & (col("l_returnflag") == values_of_interest[3][2])
+    )
+)
+
+df_explicit_filter = df_lineitem.filter(filter_expr)
+
+num_rows = df_explicit_filter.count()
+print(
+    f"Explicit filtering has number {num_rows} rows and took {time.time() - start_time} s"
+)
+start_time = time.time()
+
+# Instead try a python UDF
+
+
+def is_of_interest_impl(
+    partkey_arr: pa.Array,
+    suppkey_arr: pa.Array,
+    returnflag_arr: pa.Array,
+) -> pa.Array:
+    result = []
+    for idx, partkey in enumerate(partkey_arr):
+        partkey = partkey.as_py()
+        suppkey = suppkey_arr[idx].as_py()
+        returnflag = returnflag_arr[idx].as_py()
+        value = (partkey, suppkey, returnflag)
+        result.append(value in values_of_interest)
+
+    return pa.array(result)
+
+
+is_of_interest = udf(
+    is_of_interest_impl,
+    [pa.int32(), pa.int32(), pa.utf8()],
+    pa.bool_(),
+    "stable",
+)
+
+df_udf_filter = df_lineitem.filter(
+    is_of_interest(col("l_partkey"), col("l_suppkey"), col("l_returnflag"))
+)
+
+num_rows = df_udf_filter.count()
+print(f"UDF filtering has number {num_rows} rows and took {time.time() - start_time} s")
+start_time = time.time()
+
+# Now use a user defined function but lean on the built in pyarrow array
+# functions so we never convert rows to python objects.
+
+# To see other pyarrow compute functions see
+# https://arrow.apache.org/docs/python/api/compute.html
+#
+# It is important that the number of rows in the returned array
+# matches the original array, so we cannot use functions like
+# filtered_partkey_arr.filter(filtered_suppkey_arr).
+
+
+def udf_using_pyarrow_compute_impl(
+    partkey_arr: pa.Array,
+    suppkey_arr: pa.Array,
+    returnflag_arr: pa.Array,
+) -> pa.Array:
+    results = None
+    for partkey, suppkey, returnflag in values_of_interest:
+        filtered_partkey_arr = pc.equal(partkey_arr, partkey)
+        filtered_suppkey_arr = pc.equal(suppkey_arr, suppkey)
+        filtered_returnflag_arr = pc.equal(returnflag_arr, returnflag)
+
+        resultant_arr = pc.and_(filtered_partkey_arr, filtered_suppkey_arr)
+        resultant_arr = pc.and_(resultant_arr, filtered_returnflag_arr)
+
+        if results is None:
+            results = resultant_arr
+        else:
+            results = pc.or_(results, resultant_arr)
+
+    return results
+
+
+udf_using_pyarrow_compute = udf(
+    udf_using_pyarrow_compute_impl,
+    [pa.int32(), pa.int32(), pa.utf8()],
+    pa.bool_(),
+    "stable",
+)
+
+df_udf_pyarrow_compute = df_lineitem.filter(
+    udf_using_pyarrow_compute(col("l_partkey"), col("l_suppkey"), col("l_returnflag"))
+)
+
+num_rows = df_udf_pyarrow_compute.count()
+print(
+    f"UDF filtering using pyarrow compute has number {num_rows} rows and took {time.time() - start_time} s"
+)
+start_time = time.time()