1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
<!---
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.
-->
## Apache Arrow C++ Compute Functions
This submodule contains analytical functions that process primarily Arrow
columnar data; some functions can process scalar or Arrow-based array
inputs. These are intended for use inside query engines, data frame libraries,
etc.
Many functions have SQL-like semantics in that they perform elementwise or
scalar operations on whole arrays at a time. Other functions are not SQL-like
and compute results that may be a different length or whose results depend on
the order of the values.
Some basic terminology:
* We use the term "function" to refer to particular general operation that may
have many different implementations corresponding to different combinations
of types or function behavior options.
* We call a specific implementation of a function a "kernel". When executing a
function on inputs, we must first select a suitable kernel (kernel selection
is called "dispatching") corresponding to the value types of the inputs
* Functions along with their kernel implementations are collected in a
"function registry". Given a function name and argument types, we can look up
that function and dispatch to a compatible kernel.
Types of functions
* Scalar functions: elementwise functions that perform scalar operations in a
vectorized manner. These functions are generally valid for SQL-like
context. These are called "scalar" in that the functions executed consider
each value in an array independently, and the output array or arrays have the
same length as the input arrays. The result for each array cell is generally
independent of its position in the array.
* Vector functions, which produce a result whose output is generally dependent
on the entire contents of the input arrays. These functions **are generally
not valid** for SQL-like processing because the output size may be different
than the input size, and the result may change based on the order of the
values in the array. This includes things like array subselection, sorting,
hashing, and more.
* Scalar aggregate functions of which can be used in a SQL-like context
|
