I've been trying to sort a list of names alphabetically, let's say:
list=['Bob','Alice','Charlie']
print(list.index('Alice'))
1
However I'd also like to keep track of the original indexes, so this won't work:
list.sort()
print(list)
['Alice','Bob','Charlie']
print(list.index('Alice'))
0
After sorting the indexes changed; is there any way of keeping track of the original indexes? I've checked other similar questions and numpy has a solution, but not useful for str variables.
Just sort the reversed (index, name) tuples from enumerate to keep track of the elements and their indices:
>>> names = ['Bob','Alice','Charlie']
>>> sorted((name, index) for index, name in enumerate(names))
[('Alice', 1), ('Bob', 0), ('Charlie', 2)]
l = ['Bob','Alice','Charlie']
e = enumerate(l) # creates a generator of [(0, 'Bob'), (1, 'Alice'), (2, 'Charlie')]
sl = sorted(e, key=lambda x: x[1]) # [(1, 'Alice'), (0, 'Bob'), (2, 'Charlie')]
You may create another list of indices and sort that one, leaving the original untouched:
>>> a = ['Bob', 'Alice', 'Charlie']
>>> idx = range(len(a))
>>> idx
[0, 1, 2]
>>> sorted( idx, key=lambda x : a[x] )
[1, 0, 2]
>>>
You could create a nested dictionary of sorts to hold the original index and sorted value.
First I would recommend to use a proper name for your list object, list is a keyword in python.
names=['Bob','Alice','Charlie']
name_dict = {name : {'unsorted' : idx} for idx,name in enumerate(names)}
for sorted_idx, name in enumerate(sorted(names)):
name_dict[name].update({'sorted' : sorted_idx})
print(name_dict['Bob']['sorted'])
1
print(name_dict['Bob']['unsorted'])
0
print(name_dict)
{'Bob': {'unsorted': 0, 'sorted': 1},
'Alice': {'unsorted': 1, 'sorted': 0},
'Charlie': {'unsorted': 2, 'sorted': 2}}
Sort a list alphabetically and retrieve initial index elemnt in python
l=['Bob','Alice','Charlie']
def sort_and_get_first_element(list1):
list1.sort()
return list1[0]
print sort_and_get_first_element(l)
Yes, you can keep track of initial index but with different data structure
a = ['Bob','Alice','Charlie']
l = sorted(enumerate(a), key=lambda i: i[1])
print(l)
Now the sorted list that keep track of initial index is,
[(1, 'Alice'), (0, 'Bob'), (2, 'Charlie')]
