add method sortBy

README.md

@@ -428,7 +428,7 @@ R.slice(1, None, ['a', 'b', 'c', 'd']) # ['b', 'c', 'd']
 ```
 
 - [x] sort
-- [ ] sortBy
+- [x] sortBy
 - [ ] sortWith
 - [ ] split
 - [ ] splitAt

ramda/__init__.py

@@ -72,6 +72,7 @@
 from .reverse import reverse
 from .slice import slice
 from .sort import sort
+from .sortBy import sortBy
 from .sum import sum
 from .T import T
 from .tail import tail

ramda/sortBy.py

@@ -0,0 +1,19 @@
+from functools import cmp_to_key
+
+from .private._curry2 import _curry2
+
+
+def inner_sortBy(fn, arr):
+  def comparator(a, b):
+    aa = fn(a)
+    bb = fn(b)
+    if aa < bb:
+      return -1
+    elif aa > bb:
+      return 1
+    else:
+      return 0
+  return sorted(arr, key=cmp_to_key(comparator))
+
+
+sortBy = _curry2(inner_sortBy)

test/test_sortBy.py

@@ -0,0 +1,49 @@
+
+import unittest
+
+import ramda as R
+
+"""
+https://github.com/ramda/ramda/blob/master/test/sortBy.js
+"""
+
+albums = [
+    {'title': 'Art of the Fugue', 'artist': 'Glenn Gould', 'genre': 'Baroque'},
+    {'title': 'A Farewell to Kings', 'artist': 'Rush', 'genre': 'Rock'},
+    {'title': 'Timeout', 'artist': 'Dave Brubeck Quartet', 'genre': 'Jazz'},
+    {'title': 'Fly By Night', 'artist': 'Rush', 'genre': 'Rock'},
+    {'title': 'Goldberg Variations', 'artist': 'Daniel Barenboim', 'genre': 'Baroque'},
+    {'title': 'New World Symphony', 'artist': 'Leonard Bernstein', 'genre': 'Romantic'},
+    {'title': 'Romance with the Unseen', 'artist': 'Don Byron', 'genre': 'Jazz'},
+    {'title': 'Somewhere In Time', 'artist': 'Iron Maiden', 'genre': 'Metal'},
+    {'title': 'In Times of Desparation', 'artist': 'Danny Holt', 'genre': 'Modern'},
+    {'title': 'Evita', 'artist': 'Various', 'genre': 'Broadway'},
+    {'title': 'Five Leaves Left', 'artist': 'Nick Drake', 'genre': 'Folk'},
+    {'title': 'The Magic Flute', 'artist': 'John Eliot Gardiner', 'genre': 'Classical'}
+]
+
+
+class TestSortBy(unittest.TestCase):
+  def test_sorts_by_a_simple_property_of_the_objects(self):
+    sortedAlbums = R.sortBy(R.prop('title'), albums)
+    self.assertEqual(len(albums), len(sortedAlbums))
+    self.assertEqual('A Farewell to Kings', sortedAlbums[0]['title'])
+    self.assertEqual('Timeout', sortedAlbums[11]['title'])
+
+  def test_preserves_object_identity(self):
+    a = {'value': 'a'}
+    b = {'value': 'b'}
+    result = R.sortBy(R.prop('value'), [a, b])
+    self.assertEqual(a, result[0])
+    self.assertEqual(b, result[1])
+
+  def test_sorts_array_like_object(self):
+    args = (lambda *args: args)('c', 'a', 'b')
+    result = R.sortBy(R.identity, args)
+    self.assertEqual('a', result[0])
+    self.assertEqual('b', result[1])
+    self.assertEqual('c', result[2])
+
+
+if __name__ == '__main__':
+  unittest.main()