34 lines
812 B
Markdown
34 lines
812 B
Markdown
---
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title: Invert dictionary
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type: snippet
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language: python
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tags: [dictionary]
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cover: working-bee
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dateModified: 2020-11-02T19:27:07+02:00
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---
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Inverts a dictionary with non-unique hashable values.
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- Create a `collections.defaultdict` with `list` as the default value for each key.
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- Use `dictionary.items()` in combination with a loop to map the values of the dictionary to keys using `dict.append()`.
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- Use `dict()` to convert the `collections.defaultdict` to a regular dictionary.
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```py
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from collections import defaultdict
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def collect_dictionary(obj):
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inv_obj = defaultdict(list)
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for key, value in obj.items():
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inv_obj[value].append(key)
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return dict(inv_obj)
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```
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```py
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ages = {
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'Peter': 10,
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'Isabel': 10,
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'Anna': 9,
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}
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collect_dictionary(ages) # { 10: ['Peter', 'Isabel'], 9: ['Anna'] }
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```
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