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

Question

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.

jfs · Accepted Answer · 2011-04-16 02:35:28Z

3

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))

answered Apr 16, 2011 at 2:35

jfs

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Comments

Felix Kling · Accepted Answer · 2011-04-16 02:28:55Z

3

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)

answered Apr 16, 2011 at 2:28

Felix Kling

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johnsyweb · Accepted Answer · 2011-04-16 02:45:55Z

0

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)

>>> [(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.

answered Apr 16, 2011 at 2:37

johnsyweb

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