Support casting Utf8 to Boolean (apache#1738)

Author: MazterQyou

arrow/src/compute/kernels/cast.rs

@@ -135,7 +135,7 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
         (Dictionary(_, value_type), _) => can_cast_types(value_type, to_type),
         (_, Dictionary(_, value_type)) => can_cast_types(from_type, value_type),
 
-        (_, Boolean) => DataType::is_numeric(from_type),
+        (_, Boolean) => DataType::is_numeric(from_type) || from_type == &Utf8,
         (Boolean, _) => DataType::is_numeric(to_type) || to_type == &Utf8,
 
         (Utf8, LargeUtf8) => true,
@@ -252,6 +252,8 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
 ///
 /// Behavior:
 /// * Boolean to Utf8: `true` => '1', `false` => `0`
+/// * Utf8 to boolean: `true`, `yes`, `on`, `1` => `true`, `false`, `no`, `off`, `0` => `false`,
+///   short variants are accepted, other strings return null or error
 /// * Utf8 to numeric: strings that can't be parsed to numbers return null, float strings
 ///   in integer casts return null
 /// * Numeric to boolean: 0 returns `false`, any other value returns `true`
@@ -265,7 +267,6 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
 /// Unsupported Casts
 /// * To or from `StructArray`
 /// * List to primitive
-/// * Utf8 to boolean
 /// * Interval and duration
 pub fn cast(array: &ArrayRef, to_type: &DataType) -> Result<ArrayRef> {
     cast_with_options(array, to_type, &DEFAULT_CAST_OPTIONS)
@@ -368,6 +369,8 @@ macro_rules! cast_decimal_to_float {
 ///
 /// Behavior:
 /// * Boolean to Utf8: `true` => '1', `false` => `0`
+/// * Utf8 to boolean: `true`, `yes`, `on`, `1` => `true`, `false`, `no`, `off`, `0` => `false`,
+///   short variants are accepted, other strings return null or error
 /// * Utf8 to numeric: strings that can't be parsed to numbers return null, float strings
 ///   in integer casts return null
 /// * Numeric to boolean: 0 returns `false`, any other value returns `true`
@@ -381,7 +384,6 @@ macro_rules! cast_decimal_to_float {
 /// Unsupported Casts
 /// * To or from `StructArray`
 /// * List to primitive
-/// * Utf8 to boolean
 pub fn cast_with_options(
     array: &ArrayRef,
     to_type: &DataType,
@@ -589,10 +591,7 @@ pub fn cast_with_options(
             Int64 => cast_numeric_to_bool::<Int64Type>(array),
             Float32 => cast_numeric_to_bool::<Float32Type>(array),
             Float64 => cast_numeric_to_bool::<Float64Type>(array),
-            Utf8 => Err(ArrowError::CastError(format!(
-                "Casting from {:?} to {:?} not supported",
-                from_type, to_type,
-            ))),
+            Utf8 => cast_utf8_to_boolean(array, cast_options),
             _ => Err(ArrowError::CastError(format!(
                 "Casting from {:?} to {:?} not supported",
                 from_type, to_type,
@@ -1561,6 +1560,34 @@ fn cast_string_to_timestamp_ns<Offset: StringOffsetSizeTrait>(
     Ok(Arc::new(array) as ArrayRef)
 }
 
+/// Casts Utf8 to Boolean
+fn cast_utf8_to_boolean(from: &ArrayRef, cast_options: &CastOptions) -> Result<ArrayRef> {
+    let array = as_string_array(from);
+
+    let output_array = array
+        .iter()
+        .map(|value| match value {
+            Some(value) => match value.to_ascii_lowercase().trim() {
+                "t" | "tr" | "tru" | "true" | "y" | "ye" | "yes" | "on" | "1" => {
+                    Ok(Some(true))
+                }
+                "f" | "fa" | "fal" | "fals" | "false" | "n" | "no" | "of" | "off"
+                | "0" => Ok(Some(false)),
+                invalid_value => match cast_options.safe {
+                    true => Ok(None),
+                    false => Err(ArrowError::CastError(format!(
+                        "Cannot cast string '{}' to value of Boolean type",
+                        invalid_value,
+                    ))),
+                },
+            },
+            None => Ok(None),
+        })
+        .collect::<Result<BooleanArray>>()?;
+
+    Ok(Arc::new(output_array))
+}
+
 /// Cast numeric types to Boolean
 ///
 /// Any zero value returns `false` while non-zero returns `true`
@@ -2538,6 +2565,34 @@ mod tests {
         }
     }
 
+    #[test]
+    fn test_cast_utf8_to_bool() {
+        let strings = Arc::new(StringArray::from(vec![
+            "true", "false", "invalid", " Y ", "",
+        ])) as ArrayRef;
+        let casted = cast(&strings, &DataType::Boolean).unwrap();
+        let expected =
+            BooleanArray::from(vec![Some(true), Some(false), None, Some(true), None]);
+        assert_eq!(*as_boolean_array(&casted), expected);
+    }
+
+    #[test]
+    fn test_cast_with_options_utf8_to_bool() {
+        let strings = Arc::new(StringArray::from(vec![
+            "true", "false", "invalid", " Y ", "",
+        ])) as ArrayRef;
+        let casted =
+            cast_with_options(&strings, &DataType::Boolean, &CastOptions { safe: false });
+        match casted {
+            Ok(_) => panic!("expected error"),
+            Err(e) => {
+                assert!(e.to_string().contains(
+                    "Cast error: Cannot cast string 'invalid' to value of Boolean type"
+                ))
+            }
+        }
+    }
+
     #[test]
     fn test_cast_bool_to_i32() {
         let a = BooleanArray::from(vec![Some(true), Some(false), None]);