feat(api): add builtin support for relabeling columns to snake case

ibis/expr/types/relations.py

@@ -4,6 +4,7 @@
 import contextlib
 import functools
 import itertools
+import re
 import sys
 import warnings
 from keyword import iskeyword
@@ -744,7 +745,10 @@ def select(
     projection = select
 
     def relabel(
-        self, substitutions: Mapping[str, str] | Callable[[str], str | None]
+        self,
+        substitutions: Mapping[str, str]
+        | Callable[[str], str | None]
+        | Literal["snake_case"],
     ) -> Table:
         """Rename columns in the table.
 
@@ -753,7 +757,9 @@ def relabel(
         substitutions
             A mapping or function from old to new column names. If a column
             isn't in the mapping (or if the callable returns None) it is left
-            with its original name.
+            with its original name. May also pass the string ``"snake_case"``,
+            which will relabel all columns to use a ``snake_case`` naming
+            convention.
 
         Returns
         -------
@@ -764,6 +770,19 @@ def relabel(
 
         if isinstance(substitutions, Mapping):
             rename = substitutions.get
+        elif substitutions == "snake_case":
+
+            def rename(c):
+                c = c.strip()
+                if " " in c:
+                    # Handle "space case possibly with-hyphens"
+                    return "_".join(c.lower().split()).replace("-", "_")
+                # Handle PascalCase, camelCase, and kebab-case
+                c = re.sub(r"([A-Z]+)([A-Z][a-z])", r'\1_\2', c)
+                c = re.sub(r"([a-z\d])([A-Z])", r'\1_\2', c)
+                c = c.replace("-", "_")
+                return c.lower()
+
         else:
             rename = substitutions
 

ibis/tests/expr/test_table.py

@@ -370,7 +370,7 @@ def test_filter_fusion_distinct_table_objects(con):
     assert_equal(expr, expr4)
 
 
-def test_column_relabel(table):
+def test_column_relabel():
     table = api.table({"x": "int32", "y": "string", "z": "double"})
     sol = sch.schema({"x_1": "int32", "y_1": "string", "z": "double"})
 
@@ -387,6 +387,23 @@ def test_column_relabel(table):
         table.relabel({"missing": "oops"})
 
 
+def test_relabel_snake_case():
+    cases = [
+        ("cola", "cola"),
+        ("ColB", "col_b"),
+        ("colC", "col_c"),
+        ("col-d", "col_d"),
+        ("col_e", "col_e"),
+        (" Column F ", "column_f"),
+        ("Column G-with-hyphens", "column_g_with_hyphens"),
+        ("Col H notCamelCase", "col_h_notcamelcase"),
+    ]
+    t = ibis.table({c: "int" for c, _ in cases})
+    res = t.relabel("snake_case")
+    sol = t.relabel(dict(cases))
+    assert_equal(res, sol)
+
+
 def test_limit(table):
     limited = table.limit(10, offset=5)
     assert limited.op().n == 10