Merge pull request #411 from veronicaguo/update-snippets

Update `count_by`, `chunk_into_n` and `initial`

snippets/chunk_into_n.md

@@ -17,10 +17,10 @@ def chunk_into_n(lst, n):
   size = ceil(len(lst) / n)
   return list(
     map(lambda x: lst[x * size:x * size + size],
-    list(range(0, n)))
+    list(range(n)))
   )
 ```
 
 ```py
-chunk_into_n([1, 2, 3, 4, 5, 6, 7], 4)) # [[1, 2], [3, 4], [5, 6], [7]]
+chunk_into_n([1, 2, 3, 4, 5, 6, 7], 4) # [[1, 2], [3, 4], [5, 6], [7]]
 ```

snippets/count_by.md

@@ -5,15 +5,18 @@ tags: list,intermediate
 
 Groups the elements of a list based on the given function and returns the count of elements in each group.
 
+- Use `defaultdict()` to initialize a dictionary.
 - Use `map()` to map the values of the given list using the given function.
 - Iterate over the map and increase the element count each time it occurs.
 
 ```py
-def count_by(arr, fn=lambda x: x):
-  key = {}
-  for el in map(fn, arr):
-    key[el] = 1 if el not in key else key[el] + 1
-  return key
+from collections import defaultdict
+
+def count_by(lst, fn=lambda x: x):
+  count = defaultdict(int)
+  for val in map(fn, lst):
+    count[val] += 1
+  return dict(count)
 ```
 
 ```py

snippets/initial.md

@@ -5,11 +5,11 @@ tags: list,beginner
 
 Returns all the elements of a list except the last one.
 
-- Use `lst[0:-1]` to return all but the last element of the list.
+- Use `lst[:-1]` to return all but the last element of the list.
 
 ```py
 def initial(lst):
-  return lst[0:-1]
+  return lst[:-1]
 ```
 
 ```py