How to sort only few values inside a list in Python

Question

Suppose

A = [9, 5, 34, 33, 32, 31, 300, 30, 3, 256]

I want to sort only a particular section in a list. For example, here I want to sort only [300, 30, 3] so that overall list becomes:

A = [9, 5, 34, 33, 32, 31, 3, 30, 300, 256]

Suppose B = [300, 30, 400, 40, 500, 50, 600, 60] then after sorting it should be B = [30, 300, 40, 400, 50, 500, 60, 600].

Main idea if the leftmost digit is same 300, 30, 30 and right most digits contain only zeros then we should arrange it in increasing order.

Another example:

A = [100, 10, 1, 2000, 20, 2]

After sorting it should be A = [1, 10, 100, 2, 20, 2000]

Could anyone suggest some techniques to approach such issue. The values in my list will always be arranged in this way [200, 20, 2, 300, 30, 3, 400, 40, 4].

Code:

nums = [3, 30, 31, 32, 33, 34, 300, 256, 5, 9]
nums = sorted(nums, key=lambda x: str(x), reverse=True)
print nums
>> [9, 5, 34, 33, 32, 31, 300, 30, 3, 256]

But my final output should be [9, 5, 34, 33, 32, 31, 3, 30, 300 256].

Here is a big example:

A = [9, 5, 100, 10, 30, 3, 265, 200, 20, 2]

After sorting it should be:

A = [9, 5, 10, 100, 3, 30, 265, 2, 20, 200]

Answer 1

Since each expected sequence is contains the numbers which are a common coefficient of power of then, You can use a scientific_notation function which returns the common coefficient.Then you can categorize your numbers based on this function and concatenate them.

>>> from operator import itemgetter
>>> from itertools import chain,groupby

>>> def scientific_notation(number):
...     while number%10 == 0:
...         number = number/10
...     return number

>>> A = [9, 5, 34, 33, 32, 31, 300, 30, 3, 256]
>>> G=[list(g) for _,g in groupby(A,key=scientific_notation)] 
>>> list(chain.from_iterable(sorted(sub) if len(sub)>1 else sub for sub in G))
[9, 5, 34, 33, 32, 31, 3, 30, 300, 256]

Note that since we are categorizing the numbers based on coefficient of power of then if the length of a sub-list be more than 1 means that it's a sequence of expected numbers which need to be sort.So instead of checking the length of each sequence you can simply apply the sort on all the generators in group by:

>>> list(chain.from_iterable(sorted(g) for _,g in groupby(A,key=scientific_notation)))
[9, 5, 34, 33, 32, 31, 3, 30, 300, 256]

Answer 2

Really got twisted with this one , still don't know if it would work for all cases.

nums = [3, 30, 31, 32, 33, 34, 300, 256, 5, 9]
map(lambda x: x[1],sorted(zip(range(0,len(nums)),sorted(nums, key=lambda x: str(x), reverse=True)), key=lambda x: str(x[1]) if not str(x[1]).endswith('0') else str(str(x[1]-1)[0])+str(x[0]), reverse=True))

O/P : [9, 5, 34, 33, 32, 31, 3, 30, 300, 256]

Now I guess it would work with everything:

Earlier one wouldn't work with this nums = [30, 3, 31, 32, 33, 34, 330, 256, 5, 9]

nums = [30, 3, 31, 32, 33, 34, 330, 256, 5, 9]
map(lambda x: x[1],sorted(zip(range(0,len(nums)),sorted(nums, key=lambda x: str(x), reverse=True)), key=lambda x: str(x[1]) if not str(x[1]).endswith('0') else str(int(str(x[1]).strip("0"))-1)+str(x[0]), reverse=True))

O/P: [9, 5, 34, 33, 330, 32, 31, 3, 30, 256]

Here what I have done is taking your sorted list function , applied a zip after enumerating it So I would get [(0, 9), (1, 5), (2, 34), (3, 33), (4, 32), (5, 31), (6, 300), (7, 30), (8, 3), (9, 256)] for your input then if an element endswith a zero I would remove trailing zeros and subtract 1 and then convert it to string and append sorted index to the string which would give me a sorted list as per your case.

For e.g

Step one : zip index [(0, 9), (1, 5), (2, 34), (3, 33), (4, 32), (5, 31), (6, 300), (7, 30), (8, 3), (9, 256)]

Step two : strip trailing zeros [(0, 9), (1, 5), (2, 34), (3, 33), (4, 32), (5, 31), (6, 3), (7, 3), (8, 3), (9, 256)]

Step three : subtract 1 from those elements which had trailing zeros [(0, 9), (1, 5), (2, 34), (3, 33), (4, 32), (5, 31),(6, 3-1), (7, 3-1) (8, 3), (9, 256)]

Step four : if had trailing zeros sort them by reversed index ie first value in tuple [(0, 9), (1, 5), (2, 34), (3, 33), (4, 32), (5, 31), (8, 3), (7, 2), (6, 2), (9, 256)]

Step five : get sorted [9, 5, 34, 33, 32, 31, 3, 30, 300, 256]

OR :

More correct and Simpler solution :

sorted(map(lambda x : str(x),[9, 5, 100, 10, 30, 3, 265, 200, 20, 2]),key=lambda x : x.strip("0")+x.rjust(len(x)+(len(x)-len(x.strip("0"))),'0'),reverse=True)