From 1adde8f0eeb703ea61d5af2b4a9b65deefb6b9a4 Mon Sep 17 00:00:00 2001
From: Bo Bayles <bbayles@gmail.com>
Date: Mon, 20 Nov 2017 22:44:19 -0600
Subject: [PATCH] Add consecutive_groups()

---
 docs/api.rst                      |  1 +
 more_itertools/more.py            | 38 +++++++++++++++++++++++++++++++
 more_itertools/tests/test_more.py | 33 +++++++++++++++++++++++++++
 setup.cfg                         |  2 +-
 4 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/docs/api.rst b/docs/api.rst
index 4138bfec..8079b8cf 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -124,6 +124,7 @@ These tools return summarized or aggregated data from an iterable.
 .. autofunction:: one
 .. autofunction:: unique_to_each
 .. autofunction:: locate
+.. autofunction:: consecutive_groups
 
 ----
 
diff --git a/more_itertools/more.py b/more_itertools/more.py
index 1ba4d625..82fe0fd6 100644
--- a/more_itertools/more.py
+++ b/more_itertools/more.py
@@ -29,6 +29,7 @@
     'chunked',
     'collapse',
     'collate',
+    'consecutive_groups',
     'consumer',
     'count_cycle',
     'distinct_permutations',
@@ -1530,3 +1531,40 @@ def islice_extended(iterable, *args):
 
             for item in cache[i::step]:
                 yield item
+
+
+def consecutive_groups(iterable, ordering=lambda x: x):
+    """Yield groups of consecutive items using :func:`itertools.groupby`.
+    The *ordering* function determines whether two items are adjacent by
+    returning their position.
+
+    By default, the ordering function is the identity function. This is
+    suitable for finding runs of numbers:
+
+        >>> iterable = [1, 10, 11, 12, 20, 30, 31, 32, 33, 40]
+        >>> for group in consecutive_groups(iterable):
+        ...     print(list(group))
+        [1]
+        [10, 11, 12]
+        [20]
+        [30, 31, 32, 33]
+        [40]
+
+    For finding runs of adjacent letters, try using the :meth:`index` method
+    of a string of letters:
+
+        >>> from string import ascii_lowercase
+        >>> iterable = 'abcdfgilmnop'
+        >>> ordering = ascii_lowercase.index
+        >>> for group in consecutive_groups(iterable, ordering):
+        ...     print(list(group))
+        ['a', 'b', 'c', 'd']
+        ['f', 'g']
+        ['i']
+        ['l', 'm', 'n', 'o', 'p']
+
+    """
+    for k, g in groupby(
+        enumerate(iterable), key=lambda x: x[0] - ordering(x[1])
+    ):
+        yield map(itemgetter(1), g)
diff --git a/more_itertools/tests/test_more.py b/more_itertools/tests/test_more.py
index 333bb059..8a339c60 100644
--- a/more_itertools/tests/test_more.py
+++ b/more_itertools/tests/test_more.py
@@ -1429,3 +1429,36 @@ def test_all(self):
     def test_zero_step(self):
         with self.assertRaises(ValueError):
             list(mi.islice_extended([1, 2, 3], 0, 1, 0))
+
+
+class ConsecutiveGroupsTest(TestCase):
+    def test_numbers(self):
+        iterable = [-10, -8, -7, -6, 1, 2, 4, 5, -1, 7]
+        actual = [list(g) for g in mi.consecutive_groups(iterable)]
+        expected = [[-10], [-8, -7, -6], [1, 2], [4, 5], [-1], [7]]
+        self.assertEqual(actual, expected)
+
+    def test_custom_ordering(self):
+        iterable = ['1', '10', '11', '20', '21', '22', '30', '31']
+        ordering = lambda x: int(x)
+        actual = [list(g) for g in mi.consecutive_groups(iterable, ordering)]
+        expected = [['1'], ['10', '11'], ['20', '21', '22'], ['30', '31']]
+        self.assertEqual(actual, expected)
+
+    def test_exotic_ordering(self):
+        iterable = [
+            ('a', 'b', 'c', 'd'),
+            ('a', 'c', 'b', 'd'),
+            ('a', 'c', 'd', 'b'),
+            ('a', 'd', 'b', 'c'),
+            ('d', 'b', 'c', 'a'),
+            ('d', 'c', 'a', 'b'),
+        ]
+        ordering = list(permutations('abcd')).index
+        actual = [list(g) for g in mi.consecutive_groups(iterable, ordering)]
+        expected = [
+            [('a', 'b', 'c', 'd')],
+            [('a', 'c', 'b', 'd'), ('a', 'c', 'd', 'b'), ('a', 'd', 'b', 'c')],
+            [('d', 'b', 'c', 'a'), ('d', 'c', 'a', 'b')],
+        ]
+        self.assertEqual(actual, expected)
diff --git a/setup.cfg b/setup.cfg
index 9ae44c7d..8e57c310 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,3 +1,3 @@
 [flake8]
 exclude = ./docs/conf.py
-ignore = E731, F999
+ignore = E731, E741, F999