Add str.edit_distance_matrix (#8463)

This PR plumbs nvtext's `edit_distance_matrix` to cudf python with necessary precondition checks. It also adds python tests.

Closes #6341

Authors:
  - Michael Wang (https://github.com/isVoid)
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - Marlene  (https://github.com/marlenezw)
  - GALI PREM SAGAR (https://github.com/galipremsagar)

URL: #8463

python/cudf/cudf/_lib/cpp/nvtext/edit_distance.pxd

@@ -12,3 +12,7 @@ cdef extern from "nvtext/edit_distance.hpp" namespace "nvtext" nogil:
         const column_view & strings,
         const column_view & targets
     ) except +
+
+    cdef unique_ptr[column] edit_distance_matrix(
+        const column_view & strings
+    ) except +

python/cudf/cudf/_lib/nvtext/edit_distance.pyx

@@ -7,7 +7,8 @@ from libcpp.utility cimport move
 from cudf._lib.cpp.column.column cimport column
 from cudf._lib.cpp.column.column_view cimport column_view
 from cudf._lib.cpp.nvtext.edit_distance cimport (
-    edit_distance as cpp_edit_distance
+    edit_distance as cpp_edit_distance,
+    edit_distance_matrix as cpp_edit_distance_matrix
 )
 from cudf._lib.column cimport Column
 
@@ -21,3 +22,13 @@ def edit_distance(Column strings, Column targets):
         c_result = move(cpp_edit_distance(c_strings, c_targets))
 
     return Column.from_unique_ptr(move(c_result))
+
+
+def edit_distance_matrix(Column strings):
+    cdef column_view c_strings = strings.view()
+    cdef unique_ptr[column] c_result
+
+    with nogil:
+        c_result = move(cpp_edit_distance_matrix(c_strings))
+
+    return Column.from_unique_ptr(move(c_result))

python/cudf/cudf/core/column/string.py

@@ -17,7 +17,10 @@
 from cudf import _lib as libcudf
 from cudf._lib import string_casting as str_cast
 from cudf._lib.column import Column
-from cudf._lib.nvtext.edit_distance import edit_distance as cpp_edit_distance
+from cudf._lib.nvtext.edit_distance import (
+    edit_distance as cpp_edit_distance,
+    edit_distance_matrix as cpp_edit_distance_matrix,
+)
 from cudf._lib.nvtext.generate_ngrams import (
     generate_character_ngrams as cpp_generate_character_ngrams,
     generate_ngrams as cpp_generate_ngrams,
@@ -4859,6 +4862,47 @@ def edit_distance(self, targets) -> ParentType:
             cpp_edit_distance(self._column, targets_column)
         )
 
+    def edit_distance_matrix(self) -> ParentType:
+        """Computes the edit distance between strings in the series.
+
+        The series to compute the matrix should have more than 2 strings and
+        should not contain nulls.
+
+        Edit distance is measured based on the `Levenshtein edit distance
+        algorithm
+        <https://www.cuelogic.com/blog/the-levenshtein-algorithm>`_.
+
+
+        Returns
+        -------
+        Series of ListDtype(int64)
+            Assume `N` is the length of this series. The return series contains
+            `N` lists of size `N`, where the `j`th number in the `i`th row of
+            the series tells the edit distance between the `i`th string and the
+            `j`th string of this series.
+            The matrix is symmetric. Diagonal elements are 0.
+
+        Examples
+        --------
+        >>> import cudf
+        >>> s = cudf.Series(['abc', 'bc', 'cba'])
+        >>> s.str.edit_distance_matrix()
+        0    [0, 1, 2]
+        1    [1, 0, 2]
+        2    [2, 2, 0]
+        dtype: list
+        """
+        if self._column.size < 2:
+            raise ValueError(
+                "Require size >= 2 to compute edit distance matrix."
+            )
+        if self._column.has_nulls:
+            raise ValueError(
+                "Cannot compute edit distance between null strings. "
+                "Consider removing them using `dropna` or fill with `fillna`."
+            )
+        return self._return_or_inplace(cpp_edit_distance_matrix(self._column))
+
 
 def _massage_string_arg(value, name, allow_col=False):
     if isinstance(value, str):

python/cudf/cudf/tests/test_text.py

@@ -787,6 +787,34 @@ def test_edit_distance():
     assert_eq(expected, actual)
 
 
+def test_edit_distance_matrix():
+    # normal
+    sr = cudf.Series(["rounded", "bounded", "bounce", "trounce", "ounce"])
+
+    expected = cudf.Series(
+        [
+            [0, 1, 3, 3, 3],
+            [1, 0, 2, 4, 3],
+            [3, 2, 0, 2, 1],
+            [3, 4, 2, 0, 2],
+            [3, 3, 1, 2, 0],
+        ]
+    )
+    got = sr.str.edit_distance_matrix()
+
+    assert_eq(expected, got, check_dtype=False)
+
+    # 1-row series
+    sr2 = cudf.Series(["x"])
+    with pytest.raises(ValueError, match="Require size >= 2"):
+        sr2.str.edit_distance_matrix()
+
+    # null rows
+    sr3 = cudf.Series(["rounded", None, "bounce", "trounce", "ounce"])
+    with pytest.raises(ValueError, match="Cannot compute"):
+        sr3.str.edit_distance_matrix()
+
+
 def test_porter_stemmer_measure():
     strings = cudf.Series(
         [