Python: Sort List Specifically

[tdrusk]

Lets say I have a 2 lists
string = ['O','B','C','A','L']
key = ['C','O','B', 'A', 'L']


Now what I want to do is sort string by the indexes of key. For example, after I sort string, I want it to be ['C','O','B', 'A', 'L'].

How can I do this?

[geirha]

Would be easier if you gave each character a weight. E.g. using a dict:

weight={ 'C':0, 'O':1, 'B':2, 'A':3, 'L':4 }

Then you can use the weight as the key to sort by

string = ['O','B','C','A','L']
string.sort(key=lambda x: weight[x])


You can generate the weight from your current key list of course.


key = ['C','O','B', 'A', 'L']
weight = dict((y,x) for x,y in enumerate(key))

[tdrusk]

Would be easier if you gave each character a weight. E.g. using a dict:

weight={ 'C':0, 'O':1, 'B':2, 'A':3, 'L':4 }Then you can use the weight as the key to sort by

string = ['O','B','C','A','L']
string.sort(key=lambda x: weight[x])
You can generate the weight from your current key list of course.


key = ['C','O','B', 'A', 'L']
weight = dict((y,x) for x,y in enumerate(key))

Oh thank you :)
I saw something similar in the Python Tutorial, but I didn't quite understand it.

[diesch]

You can do it without a dict:

string.sort(key=lambda x: key.index(x))
but that's much less efficient.

[tdrusk]

Okay, now that I am working on this more I have one more question.
Consider I have 2 lists

string = ['O','B','C','A','L']
rank = [ 1 , 5 , 7, 4 , 3]
How can I sort string by the numbers in rank? For example, the output would be

string = ['O', 'L', 'A', 'B', 'C']Thanks for all the help so far. You guys are great.

[delfick]

Okay, now that I am working on this more I have one more question.
Consider I have 2 lists

string = ['O','B','C','A','L']
rank = [ 1 , 5 , 7, 4 , 3]
How can I sort string by the numbers in rank? For example, the output would be

string = ['O', 'L', 'A', 'B', 'C']Thanks for all the help so far. You guys are great.

some pseudo code for you



for each letter:
while that letter has the wrong index:
look at that letter's rank
if the rank is different than the letter's index:
swap the letter with where's it's supposed to go


However, this does depend on the ranks being equivalent to the index of each letter in the array.

If however the ranks is more of a weighting and doesn't necessarily equate to a sequence of numbers, then you can go through and normalize the ranking first.....

(for example, if ranking is [9, 20, 1, 5, 5], then normalized ranking would be [3, 4, 0, 1, 2])

:D

*returns to studies*

[diesch]

Create a list containing (rank, letter) tuples, sort that list, and get the letters:

[i[1] for i in sorted(zip(rank, string))]