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python/snippets/frequencies.md

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+---
+title: Value frequencies
+type: snippet
+tags: [list]
+cover: succulent-6
+dateModified: 2020-11-02T19:27:53+02:00
+---
+
+Creates a dictionary with the unique values of a list as keys and their frequencies as the values.
+
+- Use `collections.defaultdict` to store the frequencies of each unique element.
+- Use `dict()` to return a dictionary with the unique elements of the list as keys and their frequencies as the values.
+
+```py
+from collections import defaultdict
+
+def frequencies(lst):
+  freq = defaultdict(int)
+  for val in lst:
+    freq[val] += 1
+  return dict(freq)
+```
+
+```py
+frequencies(['a', 'b', 'a', 'c', 'a', 'a', 'b']) # { 'a': 4, 'b': 2, 'c': 1 }
+```