sweb commented on a change in pull request #9428:
URL: https://github.com/apache/arrow/pull/9428#discussion_r588464398
##########
File path: rust/datafusion/src/physical_plan/string_expressions.rs
##########
@@ -70,6 +71,16 @@ pub fn concatenate(args: &[ArrayRef]) -> Result<StringArray>
{
Ok(builder.finish())
}
+/// extract a specific group from a string column, using a regular expression
+pub fn regexp_extract(args: &[ArrayRef]) -> Result<ArrayRef> {
+ let pattern_expr = args[1].as_any().downcast_ref::<StringArray>().unwrap();
+ let pattern = pattern_expr.value(0);
+ let idx_expr = args[2].as_any().downcast_ref::<Int64Array>().unwrap();
+ let idx = idx_expr.value(0) as usize;
Review comment:
Absolutely, I did this because I am not sure, how I can get from
`ArrayRef` to `ScalarVariant` - I am looking for something like the following:
```
let pattern_expr =
args[1].as_any().downcast_ref::<ScalarValue>().unwrap();
if let ScalarValue::Utf8(Some(pattern)) = pattern_expr {
compute::regexp_match(args[0].as_ref(), pattern)
.map_err(DataFusionError::ArrowError)
} else {
Err(DataFusionError::Internal("This is wrong".to_string()))
}
```
##########
File path: rust/arrow/src/compute/kernels/regexp.rs
##########
@@ -0,0 +1,117 @@
+// 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.
+
+//! Defines kernel to extract substrings based on a regular
+//! expression of a \[Large\]StringArray
+
+use crate::array::{
+ Array, ArrayRef, GenericStringArray, GenericStringBuilder,
LargeStringArray,
+ StringArray, StringOffsetSizeTrait,
+};
+use crate::datatypes::DataType;
+use crate::error::{ArrowError, Result};
+
+use std::sync::Arc;
+
+use regex::Regex;
+
+fn generic_regexp_extract<OffsetSize: StringOffsetSizeTrait>(
+ array: &GenericStringArray<OffsetSize>,
+ re: &Regex,
+ idx: usize,
+) -> Result<ArrayRef> {
+ let mut builder: GenericStringBuilder<OffsetSize> =
GenericStringBuilder::new(0);
+
+ for maybe_value in array.iter() {
+ match maybe_value {
+ Some(value) => match re.captures(value) {
+ Some(caps) => {
+ let m = caps.get(idx).ok_or_else(|| {
+ ArrowError::ComputeError(format!(
+ "Regexp has no group with index {}",
+ idx
+ ))
+ })?;
+ builder.append_value(m.as_str())?
+ }
+ None => builder.append_null()?,
+ },
+ None => builder.append_null()?,
+ }
+ }
+ Ok(Arc::new(builder.finish()))
+}
+
+/// Extracts a specific group matched by a regular expression for a given
String array.
+/// Group index 0 returns the whole match, index 1 returns the first group and
so on. Please
+/// refer to regex crate for details on pattern specifics.
+pub fn regexp_extract(array: &Array, pattern: &str, idx: usize) ->
Result<ArrayRef> {
+ let re = Regex::new(pattern).map_err(|e| {
+ ArrowError::ComputeError(format!("Regular expression did not compile:
{:?}", e))
+ })?;
+ match array.data_type() {
+ DataType::LargeUtf8 => generic_regexp_extract(
+ array
+ .as_any()
+ .downcast_ref::<LargeStringArray>()
+ .expect("A large string is expected"),
+ &re,
+ idx,
+ ),
+ DataType::Utf8 => generic_regexp_extract(
+ array
+ .as_any()
+ .downcast_ref::<StringArray>()
+ .expect("A string is expected"),
+ &re,
+ idx,
+ ),
+ _ => Err(ArrowError::ComputeError(format!(
+ "regexp_extract does not support type {:?}",
+ array.data_type()
+ ))),
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn extract_single_group() -> Result<()> {
+ let values = vec!["abc-005-def", "X-7-5", "X545"];
+ let array = StringArray::from(values);
+ let pattern = r".*-(\d*)-.*";
+ let actual = regexp_extract(&array, pattern, 1)?;
+ let expected = StringArray::from(vec![Some("005"), Some("7"), None]);
+ let result = actual.as_any().downcast_ref::<StringArray>().unwrap();
+ assert_eq!(&expected, result);
+ Ok(())
+ }
+
+ #[test]
+ fn no_matches() -> Result<()> {
+ let values = vec!["abc", "X::50::00", "X545"];
+ let array = StringArray::from(values);
+ let pattern = r".*-(\d*)-.*";
+ let actual = regexp_extract(&array, pattern, 1)?;
+ let expected = StringArray::from(vec![None, None, None]);
+ let result = actual.as_any().downcast_ref::<StringArray>().unwrap();
+ assert_eq!(&expected, result);
+ Ok(())
+ }
Review comment:
Done
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