19 lines
547 B
Markdown
19 lines
547 B
Markdown
---
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title: intersection_by
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tags: list,function,intermediate
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---
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Returns a list of elements that exist in both 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 `b`, then use list comprehension in combination with `fn` on `a` to only keep values contained in both lists.
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```py
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def intersection_by(a, b, fn):
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_b = set(map(fn, b))
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return [item for item in a if fn(item) in _b]
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```
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```py
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from math import floor
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intersection_by([2.1, 1.2], [2.3, 3.4],floor) # [2.1]
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``` |