From e18580884579c992b250ef51d5dc27d14fde6efc Mon Sep 17 00:00:00 2001
From: priyam0k <87162535+priyam0k@users.noreply.github.com>
Date: Thu, 16 Jul 2026 04:23:27 +0530
Subject: [PATCH 1/5] feat(core): add index/columns/origin/development
 alternatives to Triangle.drop()

Route the keyword alternatives to their axis, mirroring pandas. Refs #1060.
---
 chainladder/core/pandas.py              | 58 ++++++++++++++++++++-----
 chainladder/core/tests/test_triangle.py | 31 +++++++++++++
 chainladder/core/typing.py              |  2 +-
 3 files changed, 79 insertions(+), 12 deletions(-)

diff --git a/chainladder/core/pandas.py b/chainladder/core/pandas.py
index 35a83b1b1..8c525d5cc 100644
--- a/chainladder/core/pandas.py
+++ b/chainladder/core/pandas.py
@@ -601,33 +601,69 @@ def drop(
         self,
         labels: str | int | list | None = None,
         axis: Literal["index", "columns", "origin", "development"] | int = 1,
+        index: str | int | list | None = None,
+        columns: str | int | list | None = None,
+        origin: str | int | list | None = None,
+        development: str | int | list | None = None,
     ) -> Triangle:
         """Drop specified labels from rows or columns.
 
-        Remove rows or columns by specifying label names and corresponding axis,
-        or by specifying directly index or column names.
+        Remove labels by specifying label names and corresponding axis, or by
+        specifying directly ``index``, ``columns``, ``origin``, or
+        ``development`` names.
 
         Parameters
         -----------
 
         labels:  str | int | list | None
-            Index or column labels to drop.
+            Index or column labels to drop. A single label or list-like.
 
-        axis: {0 or ‘index’, 1 or ‘columns’}, default 1
-            Whether to drop labels from the index (0 or ‘index’)
-            or columns (1 or ‘columns’).
+        axis: {0 or ‘index’, 1 or ‘columns’, 2 or 'origin', 3 or 'development'}, default 1
+            The axis to drop ``labels`` from.
+
+        index: str | int | list | None
+            Alternative to ``axis=0``. Equivalent to ``labels, axis=0``.
+
+        columns: str | int | list | None
+            Alternative to ``axis=1``. Equivalent to ``labels, axis=1``.
+
+        origin: str | int | list | None
+            Alternative to ``axis=2``. Equivalent to ``labels, axis=2``.
+
+        development: str | int | list | None
+            Alternative to ``axis=3``. Equivalent to ``labels, axis=3``.
 
         Returns
         -------
         Triangle
 
         """
-        axis = self._get_axis(axis)
-        labels = [labels] if type(labels) is str else list(labels)
-        if axis == 1:
-            return self[[item for item in self.columns if item not in labels]]
+        alternatives = {0: index, 1: columns, 2: origin, 3: development}
+        if any(value is not None for value in alternatives.values()):
+            if labels is not None:
+                raise ValueError(
+                    "Cannot specify both 'labels' and any of 'index', "
+                    "'columns', 'origin', or 'development'."
+                )
+            to_drop = {
+                ax: value for ax, value in alternatives.items() if value is not None
+            }
         else:
-            raise NotImplementedError("Triangle.drop() only implemented for column axis.")
+            to_drop = {self._get_axis(axis): labels}
+        result = self
+        for ax, ax_labels in to_drop.items():
+            ax_labels = (
+                [ax_labels] if type(ax_labels) is str else list(ax_labels)
+            )
+            if ax == 1:
+                result = result[
+                    [item for item in result.columns if item not in ax_labels]
+                ]
+            else:
+                raise NotImplementedError(
+                    "Triangle.drop() only implemented for column axis."
+                )
+        return result
 
     @property
     def T(self) -> DataFrame: # noqa: N802
diff --git a/chainladder/core/tests/test_triangle.py b/chainladder/core/tests/test_triangle.py
index 1a0857e79..16c7a2dba 100644
--- a/chainladder/core/tests/test_triangle.py
+++ b/chainladder/core/tests/test_triangle.py
@@ -338,6 +338,37 @@ def test_drop_invalid_axis_raises(clrd):
         clrd.drop(labels="CumPaidLoss", axis="bogus")
 
 
+def test_drop_columns_alternative(clrd):
+    """columns= should be equivalent to labels=..., axis=1."""
+    result = clrd.drop(columns="CumPaidLoss")
+    assert "CumPaidLoss" not in result.columns
+    assert result == clrd.drop(labels="CumPaidLoss", axis=1)
+
+
+def test_drop_columns_alternative_list(clrd):
+    """columns= should accept a list of labels."""
+    result = clrd.drop(columns=["CumPaidLoss", "IncurLoss"])
+    assert "CumPaidLoss" not in result.columns
+    assert "IncurLoss" not in result.columns
+    assert result == clrd.drop(labels=["CumPaidLoss", "IncurLoss"], axis=1)
+
+
+def test_drop_labels_and_alternative_raises(clrd):
+    """Specifying labels together with an alternative should raise ValueError."""
+    with pytest.raises(ValueError):
+        clrd.drop(labels="CumPaidLoss", columns="IncurLoss")
+
+
+def test_drop_index_origin_development_alternatives_raise(clrd):
+    """index/origin/development alternatives route to unimplemented axes."""
+    with pytest.raises(NotImplementedError):
+        clrd.drop(index="commauto")
+    with pytest.raises(NotImplementedError):
+        clrd.drop(origin="1995")
+    with pytest.raises(NotImplementedError):
+        clrd.drop(development="12")
+
+
 def test_exposure_tri():
     x = cl.load_sample("auto")
     x = x[x.development == 12]
diff --git a/chainladder/core/typing.py b/chainladder/core/typing.py
index 5f39b3332..d5231f716 100644
--- a/chainladder/core/typing.py
+++ b/chainladder/core/typing.py
@@ -97,7 +97,7 @@ def __len__(self) -> int: ...
     def get_array_module(self, arr: ArrayLike | None = None) -> ModuleType: ...
     def copy(self) -> Triangle: ...
     def set_backend(self, backend: str, inplace: bool = False, **kwargs) -> Triangle: ...
-    def drop(self, labels: str | int | list | None = None, axis: Literal["index", "columns", "origin", "development"] | int = 1) -> Triangle: ...
+    def drop(self, labels: str | int | list | None = None, axis: Literal["index", "columns", "origin", "development"] | int = 1, index: str | int | list | None = None, columns: str | int | list | None = None, origin: str | int | list | None = None, development: str | int | list | None = None) -> Triangle: ...
     def val_to_dev(self) -> Triangle: ...
     def _repr_format(self, origin_as_datetime: bool = False) -> pd.DataFrame: ...
     def _slice(self, key: pd.Series | np.ndarray, axis: Literal['ddims', 'odims']) -> Triangle: ...

From a1e721b5123716416cfb0342e68b17f8a61bd5ac Mon Sep 17 00:00:00 2001
From: priyam0k <87162535+priyam0k@users.noreply.github.com>
Date: Wed, 22 Jul 2026 11:45:17 +0530
Subject: [PATCH 2/5] docs(core): add drop() examples and wrap
 TriangleProtocol.drop signature

Address review on #1131: format the long drop() signature one arg per line and add testable Examples to the docstring.
---
 chainladder/core/pandas.py | 29 +++++++++++++++++++++++++++++
 chainladder/core/typing.py | 10 +++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/chainladder/core/pandas.py b/chainladder/core/pandas.py
index 8c525d5cc..c1e571ad1 100644
--- a/chainladder/core/pandas.py
+++ b/chainladder/core/pandas.py
@@ -637,6 +637,35 @@ def drop(
         -------
         Triangle
 
+        Examples
+        --------
+
+        Drop a single column with the ``labels``/``axis`` form or the
+        ``columns`` alternative; the two are equivalent.
+
+        .. testsetup::
+
+            import chainladder as cl
+
+        .. testcode::
+
+            tri = cl.load_sample('clrd')
+            print(tri.drop(columns='CumPaidLoss').columns.tolist())
+
+        .. testoutput::
+
+            ['IncurLoss', 'BulkLoss', 'EarnedPremDIR', 'EarnedPremCeded', 'EarnedPremNet']
+
+        A list of labels can be dropped from an axis as well.
+
+        .. testcode::
+
+            print(tri.drop(columns=['CumPaidLoss', 'IncurLoss']).columns.tolist())
+
+        .. testoutput::
+
+            ['BulkLoss', 'EarnedPremDIR', 'EarnedPremCeded', 'EarnedPremNet']
+
         """
         alternatives = {0: index, 1: columns, 2: origin, 3: development}
         if any(value is not None for value in alternatives.values()):
diff --git a/chainladder/core/typing.py b/chainladder/core/typing.py
index d5231f716..ae0405193 100644
--- a/chainladder/core/typing.py
+++ b/chainladder/core/typing.py
@@ -97,7 +97,15 @@ def __len__(self) -> int: ...
     def get_array_module(self, arr: ArrayLike | None = None) -> ModuleType: ...
     def copy(self) -> Triangle: ...
     def set_backend(self, backend: str, inplace: bool = False, **kwargs) -> Triangle: ...
-    def drop(self, labels: str | int | list | None = None, axis: Literal["index", "columns", "origin", "development"] | int = 1, index: str | int | list | None = None, columns: str | int | list | None = None, origin: str | int | list | None = None, development: str | int | list | None = None) -> Triangle: ...
+    def drop(
+        self,
+        labels: str | int | list | None = None,
+        axis: Literal["index", "columns", "origin", "development"] | int = 1,
+        index: str | int | list | None = None,
+        columns: str | int | list | None = None,
+        origin: str | int | list | None = None,
+        development: str | int | list | None = None,
+    ) -> Triangle: ...
     def val_to_dev(self) -> Triangle: ...
     def _repr_format(self, origin_as_datetime: bool = False) -> pd.DataFrame: ...
     def _slice(self, key: pd.Series | np.ndarray, axis: Literal['ddims', 'odims']) -> Triangle: ...

From 2a7c50ef556265cabc784130532ce4846dfdb665 Mon Sep 17 00:00:00 2001
From: priyam0k <87162535+priyam0k@users.noreply.github.com>
Date: Wed, 22 Jul 2026 11:54:03 +0530
Subject: [PATCH 3/5] fix(core): handle integer labels in Triangle.drop()

Normalize any scalar (str or int) into a list so a bare int routes to its axis instead of raising TypeError. Addresses Bugbot review on #1131.
---
 chainladder/core/pandas.py              | 4 +++-
 chainladder/core/tests/test_triangle.py | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/chainladder/core/pandas.py b/chainladder/core/pandas.py
index c1e571ad1..704ecc7b3 100644
--- a/chainladder/core/pandas.py
+++ b/chainladder/core/pandas.py
@@ -682,7 +682,9 @@ def drop(
         result = self
         for ax, ax_labels in to_drop.items():
             ax_labels = (
-                [ax_labels] if type(ax_labels) is str else list(ax_labels)
+                list(ax_labels)
+                if isinstance(ax_labels, (list, tuple))
+                else [ax_labels]
             )
             if ax == 1:
                 result = result[
diff --git a/chainladder/core/tests/test_triangle.py b/chainladder/core/tests/test_triangle.py
index 16c7a2dba..81f04cd1d 100644
--- a/chainladder/core/tests/test_triangle.py
+++ b/chainladder/core/tests/test_triangle.py
@@ -369,6 +369,12 @@ def test_drop_index_origin_development_alternatives_raise(clrd):
         clrd.drop(development="12")
 
 
+def test_drop_integer_label_routes_to_axis(clrd):
+    """A bare int label should route to its axis, not raise TypeError."""
+    with pytest.raises(NotImplementedError):
+        clrd.drop(development=12)
+
+
 def test_exposure_tri():
     x = cl.load_sample("auto")
     x = x[x.development == 12]

From 815783001dd511e4985933e978c3a37f7d636cbc Mon Sep 17 00:00:00 2001
From: priyam0k <87162535+priyam0k@users.noreply.github.com>
Date: Wed, 22 Jul 2026 12:07:32 +0530
Subject: [PATCH 4/5] fix(core): preserve list-like handling in Triangle.drop()

Use np.isscalar so pd.Index/ndarray labels pass through list() while scalars (str/int) are wrapped, and a bare drop() still raises. Addresses Bugbot review on #1131.
---
 chainladder/core/pandas.py              | 4 +---
 chainladder/core/tests/test_triangle.py | 9 +++++++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/chainladder/core/pandas.py b/chainladder/core/pandas.py
index 704ecc7b3..20c05be5d 100644
--- a/chainladder/core/pandas.py
+++ b/chainladder/core/pandas.py
@@ -682,9 +682,7 @@ def drop(
         result = self
         for ax, ax_labels in to_drop.items():
             ax_labels = (
-                list(ax_labels)
-                if isinstance(ax_labels, (list, tuple))
-                else [ax_labels]
+                [ax_labels] if np.isscalar(ax_labels) else list(ax_labels)
             )
             if ax == 1:
                 result = result[
diff --git a/chainladder/core/tests/test_triangle.py b/chainladder/core/tests/test_triangle.py
index 81f04cd1d..2a7ceb5f5 100644
--- a/chainladder/core/tests/test_triangle.py
+++ b/chainladder/core/tests/test_triangle.py
@@ -375,6 +375,15 @@ def test_drop_integer_label_routes_to_axis(clrd):
         clrd.drop(development=12)
 
 
+def test_drop_columns_alternative_index_like(clrd):
+    """columns= should accept list-likes such as pd.Index and ndarray."""
+    labels = clrd.columns[:2]
+    result = clrd.drop(columns=labels)
+    assert all(label not in result.columns for label in labels)
+    assert result == clrd.drop(columns=list(labels))
+    assert result == clrd.drop(columns=labels.values)
+
+
 def test_exposure_tri():
     x = cl.load_sample("auto")
     x = x[x.development == 12]

From 65f70d05f21742774de8df3b40edb3a165380a2b Mon Sep 17 00:00:00 2001
From: priyam0k <87162535+priyam0k@users.noreply.github.com>
Date: Thu, 23 Jul 2026 22:21:09 +0530
Subject: [PATCH 5/5] docs(core): show original columns in drop() example

Print the triangle's original columns before the drop, per review on #1131.
---
 chainladder/core/pandas.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/chainladder/core/pandas.py b/chainladder/core/pandas.py
index 20c05be5d..d0f98eeb9 100644
--- a/chainladder/core/pandas.py
+++ b/chainladder/core/pandas.py
@@ -650,10 +650,12 @@ def drop(
         .. testcode::
 
             tri = cl.load_sample('clrd')
+            print(tri.columns.tolist())
             print(tri.drop(columns='CumPaidLoss').columns.tolist())
 
         .. testoutput::
 
+            ['IncurLoss', 'CumPaidLoss', 'BulkLoss', 'EarnedPremDIR', 'EarnedPremCeded', 'EarnedPremNet']
             ['IncurLoss', 'BulkLoss', 'EarnedPremDIR', 'EarnedPremCeded', 'EarnedPremNet']
 
         A list of labels can be dropped from an axis as well.