Zip is its own inverse
This post is part of the programming series.
You can undo the zipping operation using
Let’s explore that in Python.
By using the unpacking operator
* you don’t have to manually specify the number of arguments (although I do assume the return of two components in the example below).
In Python 3, the zip operator returns a generator instead of a list, so you need to explicitly cast to a list if you want one.
>>> a = [1, 3] >>> b = [2, 4] >>> c = list(zip(a,b)) >>> c [(1, 2), (3, 4)] >>> a, b = list(zip(*c)) >>> a (1, 3) >>> b (2, 4)
The inverse operation will always return tuples in Python, so if your original input was a list, you also need to convert back the results to a list.
This operation is super handy.
For example, I wrote a class to recommend relevant texts for a query document based on their distance in a vector space.
recommend() function of this class returns a list of recommended texts and a list of tuples containing relevant metadata about those texts.
So the metadata will be a list of
(distance, document_id, type) tuples.
We may be interested in easily retrieving all distances, document_ids etc. as a list of their own.
We can do that by using the unpack+zip trick:
distances, document_ids, types = zip(*meta)
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