Merge pull request #188 from 30-seconds/new-list-snippets

New list snippets

for_each.md

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+---
+title: for_each
+tags: list,beginner
+---
+
+Executes the provided function once for each list element.
+
+Use a `for` loop to execute `fn` for each element in `itr`.
+
+```py
+def for_each(itr, fn):
+  for el in itr:
+    fn(el)
+```
+
+```py
+for_each([1, 2, 3], print) # 1 2 3
+```

for_each_right.md

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+---
+title: for_each_right
+tags: list,beginner
+---
+
+Executes the provided function once for each list element, starting from the list's last element.
+
+Use a `for` loop in combination with slice notation to execute `fn` for each element in `itr`, starting from the last one.
+
+```py
+def for_each_right(itr, fn):
+  for el in itr[::-1]:
+    fn(el)
+```
+
+```py
+for_each_right([1, 2, 3], print) # 3 2 1
+```

frequencies.md

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+---
+title: frequencies
+tags: list,intermediate
+---
+
+Returns a dictionary with the unique values of a list as keys and their frequencies as the values.
+
+Use a `for` loop to populate a dictionary, `f`, with the unique values in `lst` as keys, adding to existing keys every time the same value is encountered.
+
+```py
+from functools import reduce
+
+def frequencies(lst):
+  f = {}
+  for x in lst:
+    f[x] = f[x] + 1 if x in f else 1
+  return f
+```
+
+```py
+frequencies(['a', 'b', 'a', 'c', 'a', 'a', 'b']) # { 'a': 4, 'b': 2, 'c': 1 }
+```

have_same_contents.md

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+---
+title: have_same_contents
+tags: list,intermediate
+---
+
+Returns `True` if two lists contain the same elements regardless of order, `False` otherwise.
+
+Use `set()` on the combination of both lists to find the unique values.
+Iterate over them with a `for` loop comparing the `count()` of each unique value in each list.
+Return `False` if the counts do not match for any element, `True` otherwise.
+
+```py
+def have_same_contents(a, b):
+  for v in set(a + b):
+    if a.count(v) != b.count(v):
+      return False
+  return True
+```
+
+```py
+have_same_contents([1, 2, 4], [2, 4, 1]) # True
+```

includes_all.md

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+---
+title: includes_all
+tags: utility,intermediate
+---
+
+Returns `True` if all the elements in `values` are included in `lst`, `False` otherwise.
+
+Check if every value in `values` is contained in `lst` using a `for` loop, returning `False` if any one value is not found, `True` otherwise.
+
+```py
+def includes_all(lst, values):
+  for v in values:
+    if v not in lst:
+      return False
+  return True
+```
+
+```py
+includes_all([1, 2, 3, 4], [1, 4]) # True
+includes_all([1, 2, 3, 4], [1, 5]) # False
+```

includes_any.md

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+---
+title: includes_any
+tags: list,intermediate
+---
+
+Returns `True` if any element in `values` is included in `lst`, `False` otherwise.
+
+Check if any value in `values` is contained in `lst` using a `for` loop, returning `True` if any one value is found, `False` otherwise.
+
+```py
+def includes_any(lst, values):
+  for v in values:
+    if v in lst:
+      return True
+  return False
+```
+
+```py
+includes_any([1, 2, 3, 4], [2, 9]) # True
+includes_any([1, 2, 3, 4], [8, 9]) # False
+```