[FEAT] Add str.capitalize() function

daft/daft.pyi

@@ -895,6 +895,7 @@ class PyExpr:
     def utf8_lstrip(self) -> PyExpr: ...
     def utf8_rstrip(self) -> PyExpr: ...
     def utf8_reverse(self) -> PyExpr: ...
+    def utf8_capitalize(self) -> PyExpr: ...
     def image_decode(self) -> PyExpr: ...
     def image_encode(self, image_format: ImageFormat) -> PyExpr: ...
     def image_resize(self, w: int, h: int) -> PyExpr: ...
@@ -978,6 +979,7 @@ class PySeries:
     def utf8_lstrip(self) -> PySeries: ...
     def utf8_rstrip(self) -> PySeries: ...
     def utf8_reverse(self) -> PySeries: ...
+    def utf8_capitalize(self) -> PySeries: ...
     def is_nan(self) -> PySeries: ...
     def dt_date(self) -> PySeries: ...
     def dt_day(self) -> PySeries: ...

daft/expressions/expressions.py

@@ -808,6 +808,17 @@ def reverse(self) -> Expression:
         """
         return Expression._from_pyexpr(self._expr.utf8_reverse())
 
+    def capitalize(self) -> Expression:
+        """Capitalize a UTF-8 string
+
+        Example:
+            >>> col("x").str.capitalize()
+
+        Returns:
+            Expression: a String expression which is `self` uppercased with the first character and lowercased the rest
+        """
+        return Expression._from_pyexpr(self._expr.utf8_capitalize())
+
 
 class ExpressionListNamespace(ExpressionNamespace):
     def join(self, delimiter: str | Expression) -> Expression:

daft/series.py

@@ -613,6 +613,10 @@ def reverse(self) -> Series:
         assert self._series is not None
         return Series._from_pyseries(self._series.utf8_reverse())
 
+    def capitalize(self) -> Series:
+        assert self._series is not None
+        return Series._from_pyseries(self._series.utf8_capitalize())
+
 
 class SeriesDateNamespace(SeriesNamespace):
     def date(self) -> Series:

docs/source/api_docs/expressions.rst

@@ -104,6 +104,7 @@ The following methods are available under the ``expr.str`` attribute.
    Expression.str.lstrip
    Expression.str.rstrip
    Expression.str.reverse
+   Expression.str.capitalize
 
 .. _api-expressions-temporal:
 

src/daft-core/src/array/ops/utf8.rs

@@ -211,6 +211,31 @@ impl Utf8Array {
         Ok(Utf8Array::from((self.name(), Box::new(arrow_result))))
     }
 
+    pub fn capitalize(&self) -> DaftResult<Utf8Array> {
+        let self_arrow = self.as_arrow();
+        let arrow_result = self_arrow
+            .iter()
+            .map(|val| {
+                let v = val?;
+                let mut chars = v.chars();
+                match chars.next() {
+                    None => Some(String::new()),
+                    Some(first) => {
+                        let firstchar = first.to_uppercase();
+                        let mut res = String::with_capacity(v.len());
+                        res.extend(firstchar);
+                        for c in chars {
+                            res.extend(c.to_lowercase());
+                        }
+                        Some(res)
+                    }
+                }
+            })
+            .collect::<arrow2::array::Utf8Array<i64>>()
+            .with_validity(self_arrow.validity().cloned());
+        Ok(Utf8Array::from((self.name(), Box::new(arrow_result))))
+    }
+
     fn binary_broadcasted_compare<ScalarKernel>(
         &self,
         other: &Self,

src/daft-core/src/python/series.rs

@@ -288,6 +288,10 @@ impl PySeries {
         Ok(self.series.utf8_reverse()?.into())
     }
 
+    pub fn utf8_capitalize(&self) -> PyResult<Self> {
+        Ok(self.series.utf8_capitalize()?.into())
+    }
+
     pub fn is_nan(&self) -> PyResult<Self> {
         Ok(self.series.is_nan()?.into())
     }

src/daft-core/src/series/ops/utf8.rs

@@ -100,4 +100,14 @@ impl Series {
             ))),
         }
     }
+
+    pub fn utf8_capitalize(&self) -> DaftResult<Series> {
+        match self.data_type() {
+            DataType::Utf8 => Ok(self.utf8()?.capitalize()?.into_series()),
+            DataType::Null => Ok(self.clone()),
+            dt => Err(DaftError::TypeError(format!(
+                "Capitalize not implemented for type {dt}"
+            ))),
+        }
+    }
 }

src/daft-dsl/src/functions/utf8/capitalize.rs

@@ -0,0 +1,46 @@
+use daft_core::{
+    datatypes::{DataType, Field},
+    schema::Schema,
+    series::Series,
+};
+
+use crate::Expr;
+use common_error::{DaftError, DaftResult};
+
+use super::super::FunctionEvaluator;
+
+pub(super) struct CapitalizeEvaluator {}
+
+impl FunctionEvaluator for CapitalizeEvaluator {
+    fn fn_name(&self) -> &'static str {
+        "capitalize"
+    }
+
+    fn to_field(&self, inputs: &[Expr], schema: &Schema, _: &Expr) -> DaftResult<Field> {
+        match inputs {
+            [data] => match data.to_field(schema) {
+                Ok(data_field) => match &data_field.dtype {
+                    DataType::Utf8 => Ok(Field::new(data_field.name, DataType::Utf8)),
+                    _ => Err(DaftError::TypeError(format!(
+                        "Expects input to capitalize to be utf8, but received {data_field}",
+                    ))),
+                },
+                Err(e) => Err(e),
+            },
+            _ => Err(DaftError::SchemaMismatch(format!(
+                "Expected 1 input args, got {}",
+                inputs.len()
+            ))),
+        }
+    }
+
+    fn evaluate(&self, inputs: &[Series], _: &Expr) -> DaftResult<Series> {
+        match inputs {
+            [data] => data.utf8_capitalize(),
+            _ => Err(DaftError::ValueError(format!(
+                "Expected 1 input args, got {}",
+                inputs.len()
+            ))),
+        }
+    }
+}

src/daft-dsl/src/functions/utf8/mod.rs

@@ -1,3 +1,4 @@
+mod capitalize;
 mod contains;
 mod endswith;
 mod length;
@@ -9,6 +10,7 @@ mod split;
 mod startswith;
 mod upper;
 
+use capitalize::CapitalizeEvaluator;
 use contains::ContainsEvaluator;
 use endswith::EndswithEvaluator;
 use length::LengthEvaluator;
@@ -37,6 +39,7 @@ pub enum Utf8Expr {
     Lstrip,
     Rstrip,
     Reverse,
+    Capitalize,
 }
 
 impl Utf8Expr {
@@ -54,6 +57,7 @@ impl Utf8Expr {
             Lstrip => &LstripEvaluator {},
             Rstrip => &RstripEvaluator {},
             Reverse => &ReverseEvaluator {},
+            Capitalize => &CapitalizeEvaluator {},
         }
     }
 }
@@ -127,3 +131,10 @@ pub fn reverse(data: &Expr) -> Expr {
         inputs: vec![data.clone()],
     }
 }
+
+pub fn capitalize(data: &Expr) -> Expr {
+    Expr::Function {
+        func: super::FunctionExpr::Utf8(Utf8Expr::Capitalize),
+        inputs: vec![data.clone()],
+    }
+}

src/daft-dsl/src/python.rs

@@ -423,6 +423,11 @@ impl PyExpr {
         Ok(reverse(&self.expr).into())
     }
 
+    pub fn utf8_capitalize(&self) -> PyResult<Self> {
+        use crate::functions::utf8::capitalize;
+        Ok(capitalize(&self.expr).into())
+    }
+
     pub fn image_decode(&self) -> PyResult<Self> {
         use crate::functions::image::decode;
         Ok(decode(&self.expr).into())

tests/expressions/typing/test_str.py

@@ -93,3 +93,13 @@ def test_str_reverse():
         run_kernel=s.str.reverse,
         resolvable=True,
     )
+
+
+def test_str_capitalize():
+    s = Series.from_arrow(pa.array(["foo", "Bar", "BUZZ"]), name="arg")
+    assert_typing_resolve_vs_runtime_behavior(
+        data=[s],
+        expr=col(s.name()).str.capitalize(),
+        run_kernel=s.str.capitalize,
+        resolvable=True,
+    )

tests/series/test_utf8_ops.py

@@ -314,3 +314,27 @@ def test_series_utf8_reverse(data, expected) -> None:
     s = Series.from_arrow(pa.array(data))
     result = s.str.reverse()
     assert result.to_pylist() == expected
+
+
+@pytest.mark.parametrize(
+    ["data", "expected"],
+    [
+        (["Foo", "BarBaz", "quux"], ["Foo", "Barbaz", "Quux"]),
+        # With at least one null
+        (["Foo", None, "BarBaz", "quux"], ["Foo", None, "Barbaz", "Quux"]),
+        # With all nulls
+        ([None] * 4, [None] * 4),
+        # With at least one numeric strings
+        (["Foo", "BarBaz", "quux", "2"], ["Foo", "Barbaz", "Quux", "2"]),
+        # With all numeric strings
+        (["1", "2", "3"], ["1", "2", "3"]),
+        # With empty string
+        (["", "Foo", "BarBaz", "quux"], ["", "Foo", "Barbaz", "Quux"]),
+        # With emojis
+        (["😃😌😝", "abc😃😄😅"], ["😃😌😝", "Abc😃😄😅"]),
+    ],
+)
+def test_series_utf8_capitalize(data, expected) -> None:
+    s = Series.from_arrow(pa.array(data))
+    result = s.str.capitalize()
+    assert result.to_pylist() == expected

tests/table/utf8/test_capitalize.py

@@ -0,0 +1,10 @@
+from __future__ import annotations
+
+from daft.expressions import col
+from daft.table import MicroPartition
+
+
+def test_utf8_capitalize():
+    table = MicroPartition.from_pydict({"col": ["foo", None, "barBaz", "quux", "1"]})
+    result = table.eval_expression_list([col("col").str.capitalize()])
+    assert result.to_pydict() == {"col": ["Foo", None, "Barbaz", "Quux", "1"]}