refactor: Make pl.repeat part of the IR

crates/polars-core/src/frame/column/mod.rs

@@ -372,15 +372,18 @@ impl Column {
 
     #[inline]
     pub fn new_from_index(&self, index: usize, length: usize) -> Self {
+        if index >= self.len() {
+            return Self::full_null(self.name().clone(), length, self.dtype());
+        }
+
         match self {
-            Column::Series(s) => s.new_from_index(index, length).into(),
-            Column::Scalar(s) => {
-                if index >= s.len() {
-                    Self::full_null(s.name().clone(), length, s.dtype())
-                } else {
-                    s.resize(length).into()
-                }
+            Column::Series(s) => {
+                // SAFETY: Bounds check done before.
+                let av = unsafe { s.get_unchecked(index) };
+                let scalar = Scalar::new(self.dtype().clone(), av.into_static());
+                Self::new_scalar(self.name().clone(), scalar, length)
             },
+            Column::Scalar(s) => s.resize(length).into(),
         }
     }
 

crates/polars-plan/src/dsl/function_expr/mod.rs

@@ -47,6 +47,7 @@ pub mod pow;
 mod random;
 #[cfg(feature = "range")]
 mod range;
+mod repeat;
 #[cfg(feature = "rolling_window")]
 pub mod rolling;
 #[cfg(feature = "rolling_window_by")]
@@ -189,6 +190,7 @@ pub enum FunctionExpr {
         options: RankOptions,
         seed: Option<u64>,
     },
+    Repeat,
     #[cfg(feature = "round_series")]
     Clip {
         has_min: bool,
@@ -452,6 +454,7 @@ impl Hash for FunctionExpr {
                 a.hash(state);
                 b.hash(state);
             },
+            Repeat => {},
             #[cfg(feature = "rank")]
             Rank { options, seed } => {
                 options.hash(state);
@@ -651,6 +654,7 @@ impl Display for FunctionExpr {
             #[cfg(feature = "moment")]
             Kurtosis(..) => "kurtosis",
             ArgUnique => "arg_unique",
+            Repeat => "repeat",
             #[cfg(feature = "rank")]
             Rank { .. } => "rank",
             #[cfg(feature = "round_series")]
@@ -996,6 +1000,7 @@ impl From<FunctionExpr> for SpecialEq<Arc<dyn ColumnsUdf>> {
             #[cfg(feature = "moment")]
             Kurtosis(fisher, bias) => map!(dispatch::kurtosis, fisher, bias),
             ArgUnique => map!(dispatch::arg_unique),
+            Repeat => map_as_slice!(repeat::repeat),
             #[cfg(feature = "rank")]
             Rank { options, seed } => map!(dispatch::rank, options, seed),
             #[cfg(feature = "dtype-struct")]

crates/polars-plan/src/dsl/function_expr/repeat.rs

@@ -0,0 +1,18 @@
+use polars_core::prelude::{polars_ensure, polars_err, Column, PolarsResult};
+
+pub fn repeat(args: &[Column]) -> PolarsResult<Column> {
+    let c = &args[0];
+    let n = &args[1];
+
+    polars_ensure!(
+        n.dtype().is_integer(),
+        SchemaMismatch: "expected expression of dtype 'integer', got '{}'", n.dtype()
+    );
+
+    let first_value = n.get(0)?;
+    let n = first_value.extract::<usize>().ok_or_else(
+        || polars_err!(ComputeError: "could not parse value '{}' as a size.", first_value),
+    )?;
+
+    Ok(c.new_from_index(0, n))
+}

crates/polars-plan/src/dsl/function_expr/schema.rs

@@ -90,6 +90,7 @@ impl FunctionExpr {
             #[cfg(feature = "moment")]
             Kurtosis(..) => mapper.with_dtype(DataType::Float64),
             ArgUnique => mapper.with_dtype(IDX_DTYPE),
+            Repeat => mapper.with_same_dtype(),
             #[cfg(feature = "rank")]
             Rank { options, .. } => mapper.with_dtype(match options.method {
                 RankMethod::Average => DataType::Float64,

crates/polars-plan/src/dsl/functions/repeat.rs

@@ -5,17 +5,20 @@ use super::*;
 /// Generally you won't need this function, as `lit(value)` already represents a column containing
 /// only `value` whose length is automatically set to the correct number of rows.
 pub fn repeat<E: Into<Expr>>(value: E, n: Expr) -> Expr {
-    let function = |s: Column, n: Column| {
-        polars_ensure!(
-            n.dtype().is_integer(),
-            SchemaMismatch: "expected expression of dtype 'integer', got '{}'", n.dtype()
-        );
-        let first_value = n.get(0)?;
-        let n = first_value.extract::<usize>().ok_or_else(
-            || polars_err!(ComputeError: "could not parse value '{}' as a size.", first_value),
-        )?;
-        Ok(Some(s.new_from_index(0, n)))
+    let input = vec![value.into(), n];
+
+    let expr = Expr::Function {
+        input,
+        function: FunctionExpr::Repeat,
+        options: FunctionOptions {
+            flags: FunctionFlags::default()
+                | FunctionFlags::ALLOW_RENAME
+                | FunctionFlags::CHANGES_LENGTH,
+            ..Default::default()
+        },
     };
-    apply_binary(value.into(), n, function, GetOutput::same_type())
-        .alias(PlSmallStr::from_static("repeat"))
+
+    // @NOTE: This alias should probably not be here for consistency, but it is here for backwards
+    // compatibility until 2.0.
+    expr.alias(PlSmallStr::from_static("repeat"))
 }

crates/polars-python/src/lazyframe/visitor/expr_nodes.rs

@@ -1202,6 +1202,7 @@ pub(crate) fn into_py(py: Python<'_>, expr: &AExpr) -> PyResult<PyObject> {
                 #[cfg(feature = "repeat_by")]
                 FunctionExpr::RepeatBy => ("repeat_by",).to_object(py),
                 FunctionExpr::ArgUnique => ("arg_unique",).to_object(py),
+                FunctionExpr::Repeat => ("repeat",).to_object(py),
                 FunctionExpr::Rank {
                     options: _,
                     seed: _,