Add set_in() and update_in()

Closes #29

docs/colls.rst

@@ -192,6 +192,25 @@ Dict utils
         get_in({"a": {"b": 42}}, ["c"], "foo")  # -> "foo"
 
 
+.. function:: set_in(coll, path, value)
+
+    Creates a dictionary with a ``value`` set at specified ``path``. Original collection is not changed::
+
+        get_in({"a": {"b": 42}}, ["a", "b"], 10)
+        # -> {"a": {"b": 10}}
+
+        get_in({"a": {"b": 42}}, ["a", "c"], 10)
+        # -> {"a": {"b": 42, "c": 10}}
+
+
+.. function:: update_in(coll, path, update, default=None)
+
+    Creates a dictionary with a value at specified ``path`` updated::
+
+        update_in({"a": {}}, ["a", "cnt"], inc, default=0)
+        # -> {"a": {"cnt": 1}}
+
+
 Data manipulation
 -----------------
 

funcy/colls.py

@@ -18,7 +18,8 @@
            'walk', 'walk_keys', 'walk_values', 'select', 'select_keys', 'select_values', 'compact',
            'is_distinct', 'all', 'any', 'none', 'one', 'some',
            'zipdict', 'flip', 'project', 'izip_values', 'izip_dicts',
-           'where', 'pluck', 'pluck_attrs', 'invoke', 'get_in']
+           'where', 'pluck', 'pluck_attrs', 'invoke',
+           'get_in', 'set_in', 'update_in']
 
 
 ### Generic ops
@@ -229,6 +230,18 @@ def get_in(coll, path, default=None):
             return default
     return coll
 
+def set_in(coll, path, value):
+    if not path:
+        return value
+    else:
+        copy = coll.copy()
+        copy[path[0]] = set_in(copy.get(path[0], {}), path[1:], value)
+        return copy
+
+def update_in(coll, path, update, default=None):
+    value = update(get_in(coll, path, default))
+    return set_in(coll, path, value)
+
 
 def where(mappings, **cond):
     match = lambda m: all(m[k] == v for k, v in cond.items())

tests/test_colls.py

@@ -221,6 +221,30 @@ def test_get_in():
     assert get_in(d, ["a", "b"]) == "c"
     assert get_in(d, ["a", "f", "g"]) == "h"
 
+def test_set_in():
+    d = {
+        'a': {
+            'b': 1,
+            'c': 2,
+        },
+        'd': 5
+    }
+
+    d2 = set_in(d, ['a', 'c'], 7)
+    assert d['a']['c'] == 2
+    assert d2['a']['c'] == 7
+
+    d3 = set_in(d, ['e', 'f'], 42)
+    assert d3['e'] == {'f': 42}
+    assert d3['a'] is d['a']
+
+def test_update_in():
+    d = {'c': []}
+
+    d2 = update_in(d, ['a', 'b'], inc, default=0)
+    assert d2['a']['b'] == 1
+    assert d2['c'] is d['c']
+
 
 # These things are named differently in python 3
 try: