CODEWITHSUNDEEP
pythonsortingtuples
James
James

Reputation: 35

Sorting Lists of tuples based on a list of tuples - Python

I am trying to sort a list of tuples based on another list of tuples by a key in that list.

Say I have the following:

list1 = [(5, 'something'),(2,'bobby'),(9,'suzy'),(6,'crab')]
list2 = [('something','othervalues'),('suzy','stuff'),('bobby','otherthings')]

And from this I would receive the output soring on the first element of each tuple in list1.

sorted = [('suzy','stuff'),('something','othervalues'),('bobby','otherthings') ]

So essentially it performs an intersection and then sorts on the remaining values by the first element in the tuple of list1.

I am not sure how to go about this, so any help would be great.

Upvotes: 3

Views: 889

Answers (3)

johnsyweb
johnsyweb

Reputation: 141810

This would be easy were list2 a dict, like this:

{'bobby': 'otherthings', 'something': 'othervalues', 'suzy': 'stuff'}

Python will do the conversion for you:

>>> dict2 = dict(list2)

Then you can use a list comprehension:

>>> [(k,dict2[k]) for _,k in sorted(list1, reverse=True) if k in dict2]
[('suzy', 'stuff'), ('something', 'othervalues'), ('bobby', 'otherthings')]

N.B: sorted is a built-in Python function and a bad choice for a variable name.

Upvotes: 0

jfs
jfs

Reputation: 414235

Just do what the description says, sort a list of tuples based on another list of tuples by a key in that list:

rank = {key:rank for rank, key in list1}
print(sorted(list2, key=lambda t: rank.get(t[0]), reverse=True))

Upvotes: 3

Felix Kling
Felix Kling

Reputation: 816442

First create a dictionary from list1:

>>> order = dict(reversed(t) for t in list1)

This creates a name -> number mapping.

Then you can use the sorted method (don't name your variable this way) and a lambda expression as key:

>>> sorted(list2, key=lambda x: order[x[0]], reverse=True)
[('suzy', 'stuff'), ('something', 'othervalues'), ('bobby', 'otherthings')]

or, if you want to sort in-place:

>>> list2.sort(key=lambda x: order[x[0]], reverse=True)

Worth reading: Sorting Mini-HOW TO

Upvotes: 3

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