[GitHub] [arrow] seddonm1 commented on a change in pull request #9243: ARROW-11298: [Rust][DataFusion] Implement Postgres String Functions [WIP]

[GitBox <gi...@apache.org>]

seddonm1 commented on a change in pull request #9243:
URL: https://github.com/apache/arrow/pull/9243#discussion_r561653478



##########
File path: rust/datafusion/src/physical_plan/string_expressions.rs
##########
@@ -34,42 +34,446 @@ macro_rules! downcast_vec {
     }};
 }
 
-/// concatenate string columns together.
-pub fn concatenate(args: &[ArrayRef]) -> Result<StringArray> {
+/// Returns the numeric code of the first character of the argument.
+pub fn ascii<T: StringOffsetSizeTrait>(args: &[ArrayRef]) -> Result<Int32Array> {
+    let array = args[0]
+        .as_any()
+        .downcast_ref::<GenericStringArray<T>>()
+        .unwrap();
+    // first map is the iterator, second is for the `Option<_>`
+    Ok(array
+        .iter()
+        .map(|x| {
+            x.map(|x: &str| {
+                let mut chars = x.chars();
+                chars.next().map_or(0, |v| v as i32)
+            })
+        })
+        .collect())
+}
+
+/// Removes the longest string containing only characters in characters (a space by default) from the start and end of string.
+pub fn btrim<T: StringOffsetSizeTrait>(args: &[ArrayRef]) -> Result<StringArray> {
+    match args.len() {
+        0 => Err(DataFusionError::Internal(
+            "btrim was called with 0 arguments. It requires at least one.".to_string(),
+        )),
+        1 => {
+            let string_array = args[0]
+                .as_any()
+                .downcast_ref::<GenericStringArray<T>>()
+                .unwrap();
+
+            Ok(string_array
+                .iter()
+                .map(|x| x.map(|x: &str| x.trim()))
+                .collect())
+        }
+        2 => {
+            let string_array = args[0]
+                .as_any()
+                .downcast_ref::<GenericStringArray<T>>()
+                .unwrap();
+
+            let characters_array = args[1]
+                .as_any()
+                .downcast_ref::<GenericStringArray<T>>()
+                .unwrap();
+
+            Ok(string_array
+                .iter()
+                .enumerate()
+                .map(|(i, x)| {
+                    if characters_array.is_null(i) {
+                        None
+                    } else {
+                        x.map(|x: &str| {
+                            let chars: Vec<char> =
+                                characters_array.value(i).chars().collect();
+                            x.trim_start_matches(&chars[..])
+                                .trim_end_matches(&chars[..])
+                        })
+                    }
+                })
+                .collect())
+        }
+        other => Err(DataFusionError::Internal(format!(
+            "btrim was called with {} arguments. It requires at most two.",
+            other
+        ))),
+    }
+}
+
+/// Returns the character with the given code.
+pub fn chr(args: &[ArrayRef]) -> Result<StringArray> {
+    let array = args[0].as_any().downcast_ref::<Int64Array>().unwrap();
+    // first map is the iterator, second is for the `Option<_>`
+    Ok(array
+        .iter()
+        .map(|x: Option<i64>| {
+            x.map(|x| {
+                if x == 0 {
+                    Err(DataFusionError::Internal(
+                        "null character not permitted.".to_string(),
+                    ))
+                } else {
+                    match core::char::from_u32(x as u32) {
+                        Some(x) => Ok(x.to_string()),
+                        None => Err(DataFusionError::Internal(
+                            "requested character too large for encoding.".to_string(),
+                        )),
+                    }
+                }
+                .unwrap()

Review comment:
       I'm not sure if we should be panicing if these characters appear




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