From 48f7d805a4d72a009ae9ab45f34a7ce6843ba904 Mon Sep 17 00:00:00 2001
From: anopsy <anopsy28@gmail.com>
Date: Wed, 21 Aug 2024 12:25:57 +0200
Subject: [PATCH 1/4] dask-quantile-draft

---
 narwhals/_dask/expr.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/narwhals/_dask/expr.py b/narwhals/_dask/expr.py
index faedb6095..4dd8b9a1b 100644
--- a/narwhals/_dask/expr.py
+++ b/narwhals/_dask/expr.py
@@ -4,6 +4,7 @@
 from typing import TYPE_CHECKING
 from typing import Any
 from typing import Callable
+from typing import Literal
 from typing import NoReturn
 
 from narwhals._dask.utils import add_row_index
@@ -515,6 +516,22 @@ def len(self: Self) -> Self:
             returns_scalar=True,
         )
 
+    def quantile(
+        self: Self,
+        quantile: float,
+        interpolation: Literal["nearest", "higher", "lower", "midpoint", "linear"],
+    ) -> Self:
+        if interpolation == "nearest":
+            return self._from_call(
+                lambda _input, quantile: _input.quantile(q=quantile, method="dask"),
+                "quantile",
+                quantile,
+                returns_scalar=True,
+            )
+        else:
+            msg = "`higher`, `lower`, `midpoint`, `linear` - interpolation methods are not supported by Dask. Please use `nearest` instead."
+            raise NotImplementedError(msg)
+
     def is_first_distinct(self: Self) -> Self:
         def func(_input: Any) -> Any:
             _name = _input.name

From 76d229d83235ffbbd5be152c3b6f75222f7997ff Mon Sep 17 00:00:00 2001
From: anopsy <anopsy28@gmail.com>
Date: Wed, 21 Aug 2024 14:49:21 +0200
Subject: [PATCH 2/4] dask-expr-quantile with test

---
 narwhals/_dask/expr.py                 | 4 ++--
 tests/expr_and_series/quantile_test.py | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/narwhals/_dask/expr.py b/narwhals/_dask/expr.py
index 4dd8b9a1b..84288cf53 100644
--- a/narwhals/_dask/expr.py
+++ b/narwhals/_dask/expr.py
@@ -521,7 +521,7 @@ def quantile(
         quantile: float,
         interpolation: Literal["nearest", "higher", "lower", "midpoint", "linear"],
     ) -> Self:
-        if interpolation == "nearest":
+        if interpolation == "linear":
             return self._from_call(
                 lambda _input, quantile: _input.quantile(q=quantile, method="dask"),
                 "quantile",
@@ -529,7 +529,7 @@ def quantile(
                 returns_scalar=True,
             )
         else:
-            msg = "`higher`, `lower`, `midpoint`, `linear` - interpolation methods are not supported by Dask. Please use `nearest` instead."
+            msg = "`higher`, `lower`, `midpoint`, `nearest` - interpolation methods are not supported by Dask. Please use `linear` instead."
             raise NotImplementedError(msg)
 
     def is_first_distinct(self: Self) -> Self:
diff --git a/tests/expr_and_series/quantile_test.py b/tests/expr_and_series/quantile_test.py
index 8cb9320c7..d9064541f 100644
--- a/tests/expr_and_series/quantile_test.py
+++ b/tests/expr_and_series/quantile_test.py
@@ -26,7 +26,7 @@ def test_quantile_expr(
     expected: dict[str, list[float]],
     request: Any,
 ) -> None:
-    if "dask" in str(constructor):
+    if "dask" in str(constructor) and interpolation != "linear":
         request.applymarker(pytest.mark.xfail)
     q = 0.3
     data = {"a": [1, 3, 2], "b": [4, 4, 6], "z": [7.0, 8, 9]}

From 8b310fd4ca68d75d75e40378771f318753175e49 Mon Sep 17 00:00:00 2001
From: anopsy <anopsy28@gmail.com>
Date: Wed, 21 Aug 2024 15:09:49 +0200
Subject: [PATCH 3/4] dask-quantile with test and docs adjusted

---
 narwhals/expr.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/narwhals/expr.py b/narwhals/expr.py
index a8097a2a2..900538b04 100644
--- a/narwhals/expr.py
+++ b/narwhals/expr.py
@@ -1539,6 +1539,9 @@ def quantile(
         Note:
             pandas and Polars may have implementation differences for a given interpolation method.
 
+        Note:
+            dask has its own method to approximate quantile and it doesn't implement 'nearest', 'higher', 'lower', 'midpoint' as interpolation method - use 'linear' instead
+
         Arguments:
             quantile : float
                 Quantile between 0.0 and 1.0.

From 5b1c94cf62fce0393b7d10e29526061407a2c272 Mon Sep 17 00:00:00 2001
From: anopsy <anopsy28@gmail.com>
Date: Wed, 21 Aug 2024 17:35:38 +0200
Subject: [PATCH 4/4] dask-quantile with test and docs adjusted

---
 narwhals/expr.py | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/narwhals/expr.py b/narwhals/expr.py
index 900538b04..cabdfb4d1 100644
--- a/narwhals/expr.py
+++ b/narwhals/expr.py
@@ -1537,10 +1537,9 @@ def quantile(
         r"""Get quantile value.
 
         Note:
-            pandas and Polars may have implementation differences for a given interpolation method.
-
-        Note:
-            dask has its own method to approximate quantile and it doesn't implement 'nearest', 'higher', 'lower', 'midpoint' as interpolation method - use 'linear' instead
+            * pandas and Polars may have implementation differences for a given interpolation method.
+            * [dask](https://docs.dask.org/en/stable/generated/dask.dataframe.Series.quantile.html) has its own method to approximate quantile and it doesn't implement 'nearest', 'higher', 'lower', 'midpoint'
+            as interpolation method - use 'linear' which is closest to the native 'dask' - method.
 
         Arguments:
             quantile : float