27 lines
802 B
Markdown
27 lines
802 B
Markdown
---
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title: List symmetric difference based on function
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type: snippet
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language: python
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tags: [list]
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cover: succulent-1
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dateModified: 2020-11-02T19:28:35+02:00
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---
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Returns the symmetric difference between two lists, after applying the provided function to each list element of both.
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- Create a `set` by applying `fn` to each element in every list.
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- Use a list comprehension in combination with `fn` on each of them to only keep values not contained in the previously created set of the other.
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```py
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def symmetric_difference_by(a, b, fn):
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(_a, _b) = (set(map(fn, a)), set(map(fn, b)))
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return [item for item in a if fn(item) not in _b] + [item
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for item in b if fn(item) not in _a]
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```
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```py
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from math import floor
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symmetric_difference_by([2.1, 1.2], [2.3, 3.4], floor) # [1.2, 3.4]
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```
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