Set up basic CI, added tests, and implemented the mode function.

.editorconfig

@@ -0,0 +1,27 @@
+#
+# 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.
+#
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+
+[*.rs]
+indent_style = space
+indent_size = 4

.github/workflows/ci.yml

@@ -0,0 +1,70 @@
+# 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.
+
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - '**'
+  pull_request: {}
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install Rust toolchain components
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+
+      - id: cache-rust
+        uses: Swatinem/rust-cache@v2
+
+      - name: Run pre-commit lint checks
+        uses: pre-commit/[email protected]
+        with:
+          extra_args: --all-files --verbose
+        env:
+          PRE_COMMIT_COLOR: always
+          SKIP: test
+
+  test:
+    name: Test with Rust-${{ matrix.rust-version }}
+    strategy:
+      fail-fast: false
+      matrix:
+        rust-version: [stable, nightly]
+
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Rust toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust-version }}
+
+      - id: cache-rust
+        uses: Swatinem/rust-cache@v2
+
+      - name: Run cargo tests
+        run: cargo test --all-features

.gitignore

@@ -1,21 +1,59 @@
-# Generated by Cargo
-# will have compiled files and executables
-debug/
-target/
+# License
+# 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.
 
-# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
-# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
+# Linux perf sample data
+perf.data
+perf.data.old
+
+# IDE and editor directories
+.vscode
+.idea/
+.pytest_cache/
+
+# Python virtual environments
+venv/*
+
+# macOS
+.DS_Store
+
+# Docker volumes used for caching
+.docker
+
+# Rust build output
+target
 Cargo.lock
 
-# These are backup files generated by rustfmt
-**/*.rs.bk
+# Backup files
+*.orig
+.gdb_history
+.history
+
+# Swap files
+.*.swp
+.*.swo
+
+# Rust-specific tools
+rusty-tags.vi
 
-# MSVC Windows builds of rustc generate these, which store debugging information
-*.pdb
+# Apache release artifacts
+dev/dist
 
-# RustRover
-#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
-#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
-#  and can be added to the global gitignore or merged into this file.  For a more nuclear
-#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
-#.idea/
+# Apache RAT report files
+filtered_rat.txt
+rat.txt
+.githubchangeloggenerator.cache*

.pre-commit-config.yaml

@@ -0,0 +1,49 @@
+# 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.
+
+fail_fast: true
+
+repos:
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v4.0.1
+  hooks:
+  - id: check-yaml
+  - id: check-toml
+  - id: end-of-file-fixer
+  - id: trailing-whitespace
+  - id: check-added-large-files
+
+- repo: local
+  hooks:
+  - id: format
+    name: Format
+    entry: cargo fmt
+    types: [rust]
+    language: system
+    pass_filenames: false
+  - id: clippy
+    name: Clippy
+    entry: cargo clippy -- -D warnings
+    types: [rust]
+    language: system
+    pass_filenames: false
+  - id: test
+    name: Test
+    entry: cargo test
+    types: [rust]
+    language: system
+    pass_filenames: false

.rustfmt.toml

@@ -0,0 +1,18 @@
+# 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.
+
+max_width = 120

Cargo.toml

@@ -0,0 +1,54 @@
+# 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.
+
+[package]
+name = "datafusion-functions-extra"
+version = "0.1.0"
+edition = "2021"
+description = "Extra Functions for DataFusion"
+readme = "README.md"
+license = "Apache-2.0"
+keywords = ["datafusion", "functions-extra", "aggregations"]
+repository = "https://github.com/datafusion-contrib/datafusion-functions-extra/"
+rust-version = "1.76"
+
+[lib]
+name = "datafusion_functions_extra"
+path = "src/lib.rs"
+
+[dependencies]
+ahash = { version = "0.8", default-features = false, features = [
+    "runtime-rng",
+] }
+datafusion = "42"
+hashbrown = { version = "0.14.5", features = ["raw"] }
+log = "^0.4"
+paste = "1"
+
+[dev-dependencies]
+arrow = { version = "53.0.0", features = ["test_utils"] }
+criterion = { version = "0.5", features = ["async_tokio"] }
+insta = { version = "1.40.0", features = ["yaml"] }
+tokio = { version = "1.36", features = ["full"] }
+
+[lints.clippy]
+dbg_macro = "deny"
+print_stdout = "deny"
+
+[[bench]]
+name = "mode"
+harness = false

README.md

@@ -0,0 +1,64 @@
+# datafusion-functions-extra
+
+[![CI](https://github.com/datafusion-contrib/datafusion-functions-extra/actions/workflows/ci.yml/badge.svg?event=push)](https://github.com/datafusion-contrib/datafusion-functions-extra/actions/workflows/ci.yml?query=branch%3Amain)
+<!-- [![Crates.io](https://img.shields.io/crates/v/datafusion-functions-extra?color=green)](https://crates.io/crates/datafusion-functions-extra) -->
+
+**Note:** This is not an official Apache Software Foundation release.
+
+This crate provides extra functions for DataFusion, specifically focusing on advanced aggregations. These extensions are inspired by other projects like DuckDB and Spark SQL.
+
+To use these functions, you'll just need to call:
+
+```rust
+datafusion_functions_extra::register_all_extra_functions(&mut ctx)?;
+```
+
+# Examples
+
+```sql
+-- Create a table with various columns containing strings, integers, floats, dates, and times
+CREATE TABLE test_table (
+    utf8_col VARCHAR,
+    int64_col INT,
+    float64_col FLOAT,
+    date64_col DATE,
+    time64_col TIME
+) AS VALUES
+('apple', 1, 1.0, '2021-01-01', '01:00:00'),
+('banana', 2, 2.0, '2021-01-02', '02:00:00'),
+('apple', 2, 2.0, '2021-01-02', '02:00:00'),
+('orange', 3, 3.0, '2021-01-03', '03:00:00'),
+('banana', 3, 3.0, '2021-01-03', '03:00:00'),
+('apple', 3, 3.0, '2021-01-03', '03:00:00');
+
+-- Get the mode of the utf8_col column
+SELECT mode(utf8_col) as mode_utf8 FROM test_table;
+-- Results in
+-- +----------+
+-- | mode_utf8|
+-- +----------+
+-- | apple    |
+-- +----------+
+
+-- Get the mode of the date64_col column
+SELECT mode(date64_col) as mode_date FROM test_table;
+-- Results in
+-- +-----------+
+-- | mode_date |
+-- +-----------+
+-- | 2021-01-03|
+-- +-----------+
+
+-- Get the mode of the time64_col column
+SELECT mode(time64_col) as mode_time FROM test_table;
+-- Results in
+-- +-----------+
+-- | mode_time |
+-- +-----------+
+-- | 03:00:00  |
+-- +-----------+
+```
+
+## Done
+
+* [x] `mode(expression) -> scalar` - Returns the most frequent (mode) value from a column of data.