Python sort an array

Question

I'm trying to sort a numpy array containing classes from a variable.

groups =['(0, 10]', '(10, 20]', '(100, 110]', '(110, 120]', '(120, 130]',
         '(130, 140]', '(140, 150]', '(150, 160]', '(160, 170]', '(170, 180]', 
         '(180, 190]', '(190, 200]', '(20, 30]', '(200, 210]', '(210, 220]', 
         '(230, 240]', '(30, 40]', '(40, 50]', '(50, 60]', '(60, 70]', 
         '(70, 80]', '(80, 90]', '(90, 100]']

I want this:

groups = ['(0, 10]', '(10, 20]','(30, 40]','(40, 50]', '(50, 60]', ...]

I tried this:

sort(groups)

but nothing........

Did you convert the resulting categories to a list of strings, or are these elements still of categorical dtype in your actual code? — Alex Riley
– Alex Riley, Commented Dec 30, 2016 at 14:29

Patrick Haugh · Accepted Answer · 2016-12-30 14:13:34Z

4

The sorting function is sorted. We'll use a key function to extract the numbers and convert them to a tuple of integers.

sorted(groups, key=lambda x: tuple(map(int, x[1:-1].split(','))))

Output:

['(0, 10]', '(10, 20]', '(20, 30]', '(30, 40]', '(40, 50]', '(50, 60]',
 '(60, 70]', '(70, 80]', '(80, 90]', '(90, 100]', '(100, 110]', '(110, 120]',
'(120, 130]', '(130, 140]', '(140, 150]', '(150, 160]', '(160, 170]', 
'(170, 180]', '(180, 190]', '(190, 200]', '(200, 210]', '(210, 220]', '(230, 240]']

answered Dec 30, 2016 at 14:13

Patrick Haugh

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2 Comments

dimitrisGmk Over a year ago

It doesnt work... I want to find a way without losing the formation of the classes

Patrick Haugh Over a year ago

@dimitrisGmk what do you mean by the 'formation' of the classes? The key functions sorts them as if they were tuples but does not actually change the values. sorted creates a new list, and doesn't modify the old one.

MSeifert · Accepted Answer · 2016-12-30 14:13:00Z

2

You have to interpret your strings as tuples of numbers otherwise they will be sorted by lexicographical order (which would give the wrong result!):

def interpret_as_tuple(x):
    splitted = x.split(',')
    first = int(splitted[0].strip('( '))
    second = int(splitted[1].strip('] '))
    return first, second

groups.sort(key=interpret_as_tuple)

groups

returns:

['(0, 10]', '(10, 20]', '(20, 30]', '(30, 40]', '(40, 50]', '(50, 60]', '(60, 70]',
 '(70, 80]', '(80, 90]', '(90, 100]', '(100, 110]', '(110, 120]', '(120, 130]',
 '(130, 140]', '(140, 150]', '(150, 160]', '(160, 170]', '(170, 180]', '(180, 190]',
 '(190, 200]', '(200, 210]', '(210, 220]', '(230, 240]']

answered Dec 30, 2016 at 14:13

MSeifert

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Comments

blue note · Accepted Answer · 2016-12-30 14:11:14Z

-3

There are two problems with your elements

they are strings, not tuples of numbers
the closing ] does not match the opening (

So, you first have to convert them

groups = [eval(group[:-1] + ')') for group in groups]
print(sorted(groups))

edited Dec 30, 2016 at 14:11

answered Dec 30, 2016 at 14:09

blue note

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3 Comments

bruno desthuilliers Over a year ago

Avoid eval please.

blue note Over a year ago

I know, but can't think of a better way in this case

Patrick Haugh Over a year ago

ast.literal_eval is much safer

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