Adding replace expression

Cargo.toml

@@ -152,6 +152,7 @@ features = [
   "timezones",
   "peaks",
   "string_pad",
+  "replace",
   "cov",
   "http",
   "cloud",

__tests__/expr.test.ts

@@ -1135,7 +1135,7 @@ describe("expr.str", () => {
     expect(actual).toFrameEqual(expected);
     expect(seriesActual).toFrameEqual(expected);
   });
-  test("replace", () => {
+  test("str.replace", () => {
     const df = pl.DataFrame({
       os: ["kali-linux", "debian-linux", "ubuntu-linux", "mac-sierra"],
     });
@@ -1151,7 +1151,7 @@ describe("expr.str", () => {
     expect(actual).toFrameEqual(expected);
     expect(seriesActual).toFrameEqual(expected);
   });
-  test("replaceAll", () => {
+  test("str.replaceAll", () => {
     const df = pl.DataFrame({
       os: [
         "kali-linux-2021.3a",
@@ -1177,6 +1177,35 @@ describe("expr.str", () => {
     expect(actual).toFrameEqual(expected);
     expect(seriesActual).toFrameEqual(expected);
   });
+  test("expr.replace", () => {
+    const df = pl.DataFrame({ a: [1, 2, 2, 3] });
+    let actual = df.withColumns(pl.col("a").replace(2, 100).alias("replaced"));
+    let expected = pl.DataFrame({
+      a: [1, 2, 2, 3],
+      replaced: [1, 100, 100, 3],
+    });
+    expect(actual).toFrameEqual(expected);
+    actual = df.withColumns(
+      pl.col("a").replace([2, 3], [100, 200], -1, pl.Float64).alias("replaced"),
+    );
+    expected = pl.DataFrame({ a: [1, 2, 2, 3], replaced: [-1, 100, 100, 200] });
+    expect(actual).toFrameEqual(expected);
+    const mapping = { 2: 100, 3: 200 };
+    actual = df.withColumns(
+      pl
+        .col("a")
+        .replace({ old: mapping, default_: -1, returnDtype: pl.Int64 })
+        .alias("replaced"),
+    );
+    expected = pl.DataFrame({ a: [1, 2, 2, 3], replaced: [-1, 100, 100, 200] });
+    expect(actual).toFrameEqual(expected);
+
+    actual = df.withColumns(
+      pl.col("a").replace({ old: mapping }).alias("replaced"),
+    );
+    expected = pl.DataFrame({ a: [1, 2, 2, 3], replaced: [1, 100, 100, 200] });
+    expect(actual).toFrameEqual(expected);
+  });
   test("slice", () => {
     const df = pl.DataFrame({
       os: ["linux-kali", "linux-debian", "windows-vista"],

polars/lazy/expr/index.ts

@@ -743,6 +743,150 @@ export interface Expr
    * The column will be coerced to UInt32. Give this dtype to make the coercion a no-op.
    */
   repeatBy(by: Expr | string): Expr;
+  /**
+   * Replace values by different values.
+   * @param old - Value or sequence of values to replace.
+                  Accepts expression input. Sequences are parsed as Series, other non-expression inputs are parsed as literals.
+   * @param new_ - Value or sequence of values to replace by.
+                  Accepts expression input. Sequences are parsed as Series, other non-expression inputs are parsed as literals.
+                  Length must match the length of `old` or have length 1.
+   * @param default_ - Set values that were not replaced to this value.
+                      Defaults to keeping the original value.
+                      Accepts expression input. Non-expression inputs are parsed as literals.
+   * @param returnDtype - The data type of the resulting expression. If set to `None` (default), the data type is determined automatically based on the other inputs.
+   * @see {@link str.replace}
+   * @example
+   * Replace a single value by another value. Values that were not replaced remain unchanged.
+   * ```
+    >>> const df = pl.DataFrame({"a": [1, 2, 2, 3]});
+    >>> df.withColumns(pl.col("a").replace(2, 100).alias("replaced"));
+    shape: (4, 2)
+    ┌─────┬──────────┐
+    │ a   ┆ replaced │
+    │ --- ┆ ---      │
+    │ i64 ┆ i64      │
+    ╞═════╪══════════╡
+    │ 1   ┆ 1        │
+    │ 2   ┆ 100      │
+    │ 2   ┆ 100      │
+    │ 3   ┆ 3        │
+    └─────┴──────────┘
+   * ```
+   * Replace multiple values by passing sequences to the `old` and `new_` parameters.
+   * ```
+    >>> df.withColumns(pl.col("a").replace([2, 3], [100, 200]).alias("replaced"));
+    shape: (4, 2)
+    ┌─────┬──────────┐
+    │ a   ┆ replaced │
+    │ --- ┆ ---      │
+    │ i64 ┆ i64      │
+    ╞═════╪══════════╡
+    │ 1   ┆ 1        │
+    │ 2   ┆ 100      │
+    │ 2   ┆ 100      │
+    │ 3   ┆ 200      │
+    └─────┴──────────┘
+  * ```
+  * Passing a mapping with replacements is also supported as syntactic sugar.
+    Specify a default to set all values that were not matched.
+  * ```
+    >>> const mapping = {2: 100, 3: 200};
+    >>> df.withColumns(pl.col("a").replace({ old: mapping, default_: -1, returnDtype: pl.Int64 }).alias("replaced");
+    shape: (4, 2)
+    ┌─────┬──────────┐
+    │ a   ┆ replaced │
+    │ --- ┆ ---      │
+    │ i64 ┆ i64      │
+    ╞═════╪══════════╡
+    │ 1   ┆ -1       │
+    │ 2   ┆ 100      │
+    │ 2   ┆ 100      │
+    │ 3   ┆ 200      │
+    └─────┴──────────┘
+  * ```
+    Replacing by values of a different data type sets the return type based on
+    a combination of the `new` data type and either the original data type or the
+    default data type if it was set.
+  * ```
+    >>> const df = pl.DataFrame({"a": ["x", "y", "z"]});
+    >>> const mapping = {"x": 1, "y": 2, "z": 3};
+    >>> df.withColumns(pl.col("a").replace({ old: mapping }).alias("replaced"));
+    shape: (3, 2)
+    ┌─────┬──────────┐
+    │ a   ┆ replaced │
+    │ --- ┆ ---      │
+    │ str ┆ str      │
+    ╞═════╪══════════╡
+    │ x   ┆ 1        │
+    │ y   ┆ 2        │
+    │ z   ┆ 3        │
+    └─────┴──────────┘
+    >>> df.withColumns(pl.col("a").replace({ old: mapping, default_: None }).alias("replaced"));
+    shape: (3, 2)
+    ┌─────┬──────────┐
+    │ a   ┆ replaced │
+    │ --- ┆ ---      │
+    │ str ┆ i64      │
+    ╞═════╪══════════╡
+    │ x   ┆ 1        │
+    │ y   ┆ 2        │
+    │ z   ┆ 3        │
+    └─────┴──────────┘
+  * ```
+    Set the `returnDtype` parameter to control the resulting data type directly.
+  * ```
+    >>> df.withColumns(pl.col("a").replace({ old: mapping, returnDtype: pl.UInt8 }).alias("replaced"));
+    shape: (3, 2)
+    ┌─────┬──────────┐
+    │ a   ┆ replaced │
+    │ --- ┆ ---      │
+    │ str ┆ u8       │
+    ╞═════╪══════════╡
+    │ x   ┆ 1        │
+    │ y   ┆ 2        │
+    │ z   ┆ 3        │
+    └─────┴──────────┘
+  * ```
+  * Expression input is supported for all parameters.
+  * ```
+    >>> const df = pl.DataFrame({"a": [1, 2, 2, 3], "b": [1.5, 2.5, 5.0, 1.0]});
+    >>> df.withColumns(
+    ...         pl.col("a").replace({
+    ...         old: pl.col("a").max(),
+    ...         new_: pl.col("b").sum(),
+    ...         default_: pl.col("b"),
+    ...     }).alias("replaced")
+    ... );
+    shape: (4, 3)
+    ┌─────┬─────┬──────────┐
+    │ a   ┆ b   ┆ replaced │
+    │ --- ┆ --- ┆ ---      │
+    │ i64 ┆ f64 ┆ f64      │
+    ╞═════╪═════╪══════════╡
+    │ 1   ┆ 1.5 ┆ 1.5      │
+    │ 2   ┆ 2.5 ┆ 2.5      │
+    │ 2   ┆ 5.0 ┆ 5.0      │
+    │ 3   ┆ 1.0 ┆ 10.0     │
+    └─────┴─────┴──────────┘
+   * ``` 
+   */
+  replace(
+    old: Expr | number | number[],
+    new_: Expr | number | number[],
+    default_?: Expr | number | number[],
+    returnDtype?: DataType,
+  ): Expr;
+  replace({
+    old,
+    new_,
+    default_,
+    returnDtype,
+  }: {
+    old: unknown | Expr | number | number[];
+    new_?: Expr | number | number[];
+    default_?: Expr | number | number[];
+    returnDtype?: DataType;
+  }): Expr;
   /** Reverse the arrays in the list */
   reverse(): Expr;
   /**
@@ -1421,6 +1565,24 @@ export const _Expr = (_expr: any): Expr => {
 
       return _Expr(_expr.repeatBy(e));
     },
+    replace(old, newValue, defaultValue, returnDtype) {
+      let oldIn: any = old;
+      let newIn = newValue;
+      let defIn = defaultValue;
+      if (old && typeof old === "object" && !Array.isArray(old)) {
+        oldIn = Object.keys(old["old"]);
+        newIn = Object.values(old["old"]);
+        defIn = old["default_"];
+      }
+      return _Expr(
+        _expr.replace(
+          exprToLitOrExpr(oldIn)._expr,
+          exprToLitOrExpr(newIn)._expr,
+          defIn ? exprToLitOrExpr(defIn)._expr : undefined,
+          returnDtype,
+        ),
+      );
+    },
     reverse() {
       return _Expr(_expr.reverse());
     },

src/lazy/dsl.rs

@@ -954,7 +954,18 @@ impl JsExpr {
             .split_exact_inclusive(by.0, n as usize)
             .into()
     }
-
+    #[napi(catch_unwind)]
+    pub fn replace(&self, old: &JsExpr, new: &JsExpr, default: Option<&JsExpr>, return_dtype: Option<Wrap<DataType>>) -> JsExpr {
+        self.inner
+        .clone()
+        .replace(
+            old.inner.clone(),
+            new.inner.clone(),
+            default.map(|e| e.inner.clone()),
+            return_dtype.map(|dt| dt.0),
+        )
+        .into()
+    }
     #[napi(catch_unwind)]
     pub fn year(&self) -> JsExpr {
         self.clone().inner.dt().year().into()