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jbranchaud
47 lines
1.1 KiB
Markdown
47 lines
1.1 KiB
Markdown
# Deduplicate A List Into A Tuple
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A `list` is not hashable which means you can't use it for things like `dict`
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keys or cache keys. Instead you need to convert it into something like a `set`
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or a `tuple`.
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Here is an example list:
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```python
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>>> l1 = [3,4,1,2,5,4,1]
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```
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Turning this list into a `set` or `frozenset` is straightforward:
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```python
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>>> set(l1)
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{1, 2, 3, 4, 5}
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>>> frozenset(l1)
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frozenset({1, 2, 3, 4, 5})
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```
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If you're trying to preserve the order after deduplicating, then you'll want to
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use a `tuple` instead of a `set`. In order to deduplicate while maintaining the
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ordering, you can exploit the fact that `dict` keys maintain their order. A
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`list` can be transformed into the keys of a `dict` with
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[`dict.fromkeys`](https://docs.python.org/3/library/stdtypes.html#dict.fromkeys):
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```python
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>>> dict.fromkeys(l1)
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{3: None, 4: None, 1: None, 2: None, 5: None}
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```
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And here is your `tuple` which extracts the keys of the `dict`:
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```python
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>>> tuple(dict.fromkeys(l1))
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(3, 4, 1, 2, 5)
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```
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By comparison, here is the `tuple` transformed directly from the `list` without
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deduplication.
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```python
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>>> tuple(l1)
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(3, 4, 1, 2, 5, 4, 1)
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```
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