Optimize performance of initcap function (~2x faster)

datafusion/functions/Cargo.toml

@@ -207,3 +207,8 @@ required-features = ["unicode_expressions"]
 harness = false
 name = "trunc"
 required-features = ["math_expressions"]
+
+[[bench]]
+harness = false
+name = "initcap"
+required-features = ["string_expressions"]

datafusion/functions/benches/initcap.rs

@@ -0,0 +1,93 @@
+// 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.
+
+extern crate criterion;
+
+use arrow::array::OffsetSizeTrait;
+use arrow::datatypes::DataType;
+use arrow::util::bench_util::{
+    create_string_array_with_len, create_string_view_array_with_len,
+};
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs};
+use datafusion_functions::string;
+use std::sync::Arc;
+
+fn create_args<O: OffsetSizeTrait>(
+    size: usize,
+    str_len: usize,
+    force_view_types: bool,
+) -> Vec<ColumnarValue> {
+    if force_view_types {
+        let string_array =
+            Arc::new(create_string_view_array_with_len(size, 0.2, str_len, false));
+
+        vec![ColumnarValue::Array(string_array)]
+    } else {
+        let string_array =
+            Arc::new(create_string_array_with_len::<O>(size, 0.2, str_len));
+
+        vec![ColumnarValue::Array(string_array)]
+    }
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let initcap = string::initcap();
+    for size in [1024, 4096] {
+        let args = create_args::<i32>(size, 8, true);
+        c.bench_function(
+            format!("initcap string view shorter than 12 [size={}]", size).as_str(),
+            |b| {
+                b.iter(|| {
+                    black_box(initcap.invoke_with_args(ScalarFunctionArgs {
+                        args: args.clone(),
+                        number_rows: size,
+                        return_type: &DataType::Utf8View,
+                    }))
+                })
+            },
+        );
+
+        let args = create_args::<i32>(size, 16, true);
+        c.bench_function(
+            format!("initcap string view longer than 12 [size={}]", size).as_str(),
+            |b| {
+                b.iter(|| {
+                    black_box(initcap.invoke_with_args(ScalarFunctionArgs {
+                        args: args.clone(),
+                        number_rows: size,
+                        return_type: &DataType::Utf8View,
+                    }))
+                })
+            },
+        );
+
+        let args = create_args::<i32>(size, 16, false);
+        c.bench_function(format!("initcap string [size={}]", size).as_str(), |b| {
+            b.iter(|| {
+                black_box(initcap.invoke_with_args(ScalarFunctionArgs {
+                    args: args.clone(),
+                    number_rows: size,
+                    return_type: &DataType::Utf8,
+                }))
+            })
+        });
+    }
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

datafusion/functions/src/string/initcap.rs

@@ -132,21 +132,22 @@ fn initcap_utf8view(args: &[ArrayRef]) -> Result<ArrayRef> {
     Ok(Arc::new(result) as ArrayRef)
 }
 
-fn initcap_string(string: Option<&str>) -> Option<String> {
-    let mut char_vector = Vec::<char>::new();
-    string.map(|string: &str| {
-        char_vector.clear();
-        let mut previous_character_letter_or_number = false;
-        for c in string.chars() {
-            if previous_character_letter_or_number {
-                char_vector.push(c.to_ascii_lowercase());
+fn initcap_string(input: Option<&str>) -> Option<String> {
+    input.map(|s| {
+        let mut result = String::with_capacity(s.len());
+        let mut prev_is_alphanumeric = false;
+
+        for c in s.chars() {
+            let transformed = if prev_is_alphanumeric {
+                c.to_ascii_lowercase()
             } else {
-                char_vector.push(c.to_ascii_uppercase());
-            }
-            previous_character_letter_or_number =
-                c.is_ascii_uppercase() || c.is_ascii_lowercase() || c.is_ascii_digit();
+                c.to_ascii_uppercase()
+            };
+            result.push(transformed);
+            prev_is_alphanumeric = c.is_ascii_alphanumeric();
         }
-        char_vector.iter().collect::<String>()
+
+        result
     })
 }