Flexable Collating (feedback please)

[Ron Adam]

I put together the following module today and would like some feedback on any
obvious problems. Or even opinions of weather or not it is a good approach.

While collating is not a difficult thing to do for experienced programmers, I
have seen quite a lot of poorly sorted lists in commercial applications, so it
seems it would be good to have an easy to use ready made API for collating.

I tried to make this both easy to use and flexible. My first thoughts was to
try and target actual uses such as Phone directory sorting, or Library sorting,
etc., but it seemed using keywords to alter the behavior is both easier and more
flexible.

I think the regular expressions I used to parse leading and trailing numerals
could be improved. They work, but you will probably get inconsistent results if
the strings are not well formed. Any suggestions on this would be appreciated.

Should I try to extend it to cover dates and currency sorting? Probably those
types should be converted before sorting, but maybe sometimes it's useful
not to?

Another variation is collating dewy decimal strings. It should be easy to add
if someone thinks that might be useful.

I haven't tested this in *anything* yet, so don't plug it into production code
of any type. I also haven't done any performance testing.

See the doc tests below for examples of how it's used.

Cheers,
Ron Adam

"""
Collate.py

A general purpose configurable collate module.

Collation can be modified with the following keywords:

CAPS_FIRST -Aaa, aaa, Bbb, bbb
HYPHEN_AS_SPACE -Don't ignore hyphens
UNDERSCORE_AS_S PACE -Underscores as white space
IGNORE_LEADING_ WS -Disregard leading white space
NUMERICAL -Digit sequences as numerals
COMMA_IN_NUMERA LS -Allow commas in numerals

* See doctests for examples.

Author: Ron Adam, ro*@ronadam.com, 10/18/2006

"""
import re
import locale
locale.setlocal e(locale.LC_ALL , '') # use current locale settings

# The above line may change the string constants from the string
# module. This may have unintended effects if your program
# assumes they are always the ascii defaults.
CAPS_FIRST = 1
NUMERICAL = 2
HYPHEN_AS_SPACE = 4
UNDERSCORE_AS_S PACE = 8
IGNORE_LEADING_ WS = 16
COMMA_IN_NUMERA LS = 32

class Collate(object) :
""" A general purpose and configurable collator class.
"""
def __init__(self, flag):
self.flag = flag
def transform(self, s):
""" Transform a string for collating.
"""
if self.flag & CAPS_FIRST:
s = s.swapcase()
if self.flag & HYPHEN_AS_SPACE :
s = s.replace('-', ' ')
if self.flag & UNDERSCORE_AS_S PACE:
s = s.replace('_', ' ')
if self.flag & IGNORE_LEADING_ WS:
s = s.strip()
if self.flag & NUMERICAL:
if self.flag & COMMA_IN_NUMERA LS:
rex = re.compile('^(\ d*\,?\d*\.?\d*) (\D*)(\d*\,?\d* \.?\d*)',
re.LOCALE)
else:
rex = re.compile('^(\ d*\.?\d*)(\D*)( \d*\.?\d*)', re.LOCALE)
slist = rex.split(s)
for i, x in enumerate(slist ):
if self.flag & COMMA_IN_NUMERA LS:
x = x.replace(',', '')
try:
slist[i] = float(x)
except:
slist[i] = locale.strxfrm( x)
return slist
return locale.strxfrm( s)

def __call__(self, a, b):
""" This allows the Collate class work as a sort key.

USE: list.sort(key=C ollate(flags))
"""
return cmp(self.transf orm(a), self.transform( b))

def collate(slist, flags=0):
""" Collate list of strings in place.
"""
return slist.sort(Coll ate(flags))

def collated(slist, flags=0):
""" Return a collated list of strings.

This is a decorate-undecorate collate.
"""
collator = Collate(flags)
dd = [(collator.trans form(x), x) for x in slist]
dd.sort()
return list([B for (A, B) in dd])

def _test():
"""
DOC TESTS AND EXAMPLES:

Sort (and sorted) normally order all words beginning with caps
before all words beginning with lower case.

>>t = ['tuesday', 'Tuesday', 'Monday', 'monday']
sorted(t) # regular sort

['Monday', 'Tuesday', 'monday', 'tuesday']

Locale collation puts words beginning with caps after words
beginning with lower case of the same letter.

>>collated(t)

['monday', 'Monday', 'tuesday', 'Tuesday']

The CAPS_FIRST option can be used to put all words beginning
with caps after words beginning in lowercase of the same letter.

>>collated(t, CAPS_FIRST)

['Monday', 'monday', 'Tuesday', 'tuesday']
The HYPHEN_AS_SPACE option causes hyphens to be equal to space.

>>t = ['a-b', 'b-a', 'aa-b', 'bb-a']
collated(t)

['aa-b', 'a-b', 'b-a', 'bb-a']

>>collated(t, HYPHEN_AS_SPACE )

['a-b', 'aa-b', 'b-a', 'bb-a']
The IGNORE_LEADING_ WS and UNDERSCORE_AS_S PACE options can be
used together to improve ordering in some situations.

>>t = ['sum', '__str__', 'about', ' round']
collated(t)

[' round', '__str__', 'about', 'sum']

>>collated(t, IGNORE_LEADING_ WS)

['__str__', 'about', ' round', 'sum']

>>collated(t, UNDERSCORE_AS_S PACE)

[' round', '__str__', 'about', 'sum']

>>collated(t, IGNORE_LEADING_ WS|UNDERSCORE_A S_SPACE)

['about', ' round', '__str__', 'sum']
The NUMERICAL option orders leading and trailing digits as numerals.

>>t = ['a5', 'a40', '4abc', '20abc', 'a10.2', '13.5b', 'b2']
collated(t, NUMERICAL)

['4abc', '13.5b', '20abc', 'a5', 'a10.2', 'a40', 'b2']
The COMMA_IN_NUMERA LS option ignores commas instead of using them to
seperate numerals.

>>t = ['a5', 'a4,000', '500b', '100,000b']
collated(t, NUMERICAL|COMMA _IN_NUMERALS)

['500b', '100,000b', 'a5', 'a4,000']
Collating also can be done in place using collate() instead of collated().

>>t = ['Fred', 'Ron', 'Carol', 'Bob']
collate(t)
t

['Bob', 'Carol', 'Fred', 'Ron']

"""
import doctest
doctest.testmod ()
if __name__ == '__main__':
_test()

[Ron Adam]

Fixed...
Changed the collate() function to return None the same as sort() since it is an
in place collate.

A comment in _test() doctests was reversed. CAPS_FIRST option puts words
beginning with capitals before, not after, words beginning with lower case of
the same letter.
It seems I always find a few obvious glitches right after I post something. ;-)

Cheers,
Ron

[georgeryoung]

On Oct 18, 2:42 am, Ron Adam <r...@ronadam.c omwrote:

I put together the following module today and would like some feedback on any
obvious problems. Or even opinions of weather or not it is a good approach.

,,,
def __call__(self, a, b):
""" This allows the Collate class work as a sort key.

USE: list.sort(key=C ollate(flags))
"""
return cmp(self.transf orm(a), self.transform( b))

You document _call__ as useful for the "key" keyword to sort, but you
implement it for the "cmp" keyword. The "key" allows much better
performance, since it's called only once per value. Maybe just :
return self.transform( a)

-- George

[Ron Adam]

ge**********@gm ail.com wrote:

>
On Oct 18, 2:42 am, Ron Adam <r...@ronadam.c omwrote:

>I put together the following module today and would like some feedback on any
obvious problems. Or even opinions of weather or not it is a good approach.

,,,
def __call__(self, a, b):
""" This allows the Collate class work as a sort key.

USE: list.sort(key=C ollate(flags))
"""
return cmp(self.transf orm(a), self.transform( b))

You document _call__ as useful for the "key" keyword to sort, but you
implement it for the "cmp" keyword. The "key" allows much better
performance, since it's called only once per value. Maybe just :
return self.transform( a)

-- George

Thanks, I changed it to the following...

def __call__(self, a):
""" This allows the Collate class work as a sort key.

USE: list.sort(key=C ollate(flags))
"""
return self.transform( a)

And also changed the sort call here ...
def collate(slist, flags=0):
""" Collate list of strings in place.
"""
slist.sort(key= Collate(flags)) <<<
Today I'll do some performance tests to see how much faster it is for moderate
sized lists.
Cheers,
Ron

[bearophileHUGS]

This part of code uses integer "constants" to be or-ed (or added):

CAPS_FIRST = 1
NUMERICAL = 2
HYPHEN_AS_SPACE = 4
UNDERSCORE_AS_S PACE = 8
IGNORE_LEADING_ WS = 16
COMMA_IN_NUMERA LS = 32

....

def __init__(self, flag):
self.flag = flag
def transform(self, s):
""" Transform a string for collating.
"""
if self.flag & CAPS_FIRST:
s = s.swapcase()
if self.flag & HYPHEN_AS_SPACE :
s = s.replace('-', ' ')
if self.flag & UNDERSCORE_AS_S PACE:
s = s.replace('_', ' ')
if self.flag & IGNORE_LEADING_ WS:
s = s.strip()
if self.flag & NUMERICAL:
if self.flag & COMMA_IN_NUMERA LS:

This is used in C, but maybe for Python other solutions may be better.
I can see some different (untested) solutions:

1)

def selfassign(self , locals):
# Code from web.py, modified.
for key, value in locals.iteritem s():
if key != 'self':
setattr(self, key, value)

def __init__(self,
caps_first=Fals e,
hyphen_as_space =False,
underscore_as_s pace=False,
ignore_leading_ ws=False,
numerical=False ,
comma_in_numera ls=False):
selfassign(self , locals())

def transform(self, s):
if self.caps_first :
...

Disadvangages: if a flag is added/modified, the code has to be modified
in two places.
2)

def __init__(self, **kwds):
self.lflags = [k for k,v in kwds.items() if v]
def transform(self, s):
if "caps_first " in self.lflags:
...

This class can be created with 1 instead of Trues, to shorten the code.

Disadvantages: the user of this class has to read from the class
doctring or from from the docs the list of possible flags (and such
docs can be out of sync from the code).
3)

Tkinter (Tcl) shows that sometimes strings are better than int
constants (like using "left" instead of tkinter.LEFT, etc), so this is
another possibile solution:

def __init__(self, flags=""):
self.lflags = flags.lower().s plit()
def transform(self, s):
if "caps_first " in self.lflags:
...

An example of calling this class:

.... = Collate("caps_f irst hyphen_as_space numerical")

I like this third (nonstandard) solution enough.

Bye,
bearophile

[Ron Adam]

I made a number of changes ... (the new version is listed below)
These changes also resulted in improving the speed by about 3 times when all
flags are specified.

Collating now takes about 1/3 (or less) time. Although it is still quite a bit
slower than a bare list.sort(), that is to be expected as collate is locale
aware and does additional transformations on the data which you would need to do
anyways. The tests where done with Unicode strings as well.

Changed the flag types from integer values to a list of named strings. The
reason for this is it makes finding errors easier and you can examine the flags
attribute and get a readable list of flags.

A better regular expression for separating numerals. It now separates numerals
in the middle of the string.

Changed flag COMMA_IN_NUMERA LS to IGNORE_COMMAS, This was how it was implemented.

Added flag PERIOD_AS_COMMA S

This lets you collate decimal separated numbers correctly such as version
numbers and internet address's. It also prevents numerals from being
interpreted as floating point or decimal.

It might make more since to implement it as PERIOD_IS_SEPAR ATOR. Needed?

Other minor changes to doc strings and tests were made.
Any feedback is welcome.

Cheers,
Ron

"""
Collate.py

A general purpose configurable collate module.

Collation can be modified with the following keywords:

CAPS_FIRST -Aaa, aaa, Bbb, bbb
HYPHEN_AS_SPACE -Don't ignore hyphens
UNDERSCORE_AS_S PACE -Underscores as white space
IGNORE_LEADING_ WS -Disregard leading white space
NUMERICAL -Digit sequences as numerals
IGNORE_COMMAS -Allow commas in numerals
PERIOD_AS_COMMA S -Periods can separate numerals.

* See doctests for examples.

Author: Ron Adam, ro*@ronadam.com

"""
__version__ = '0.02 (pre-alpha) 10/18/2006'

import re
import locale
import string

locale.setlocal e(locale.LC_ALL , '') # use current locale settings

# The above line may change the string constants from the string
# module. This may have unintended effects if your program
# assumes they are always the ascii defaults.

CAPS_FIRST = 'CAPS_FIRST'
HYPHEN_AS_SPACE = 'HYPHEN_AS_SPAC E'
UNDERSCORE_AS_S PACE = 'UNDERSCORE_AS_ SPACE'
IGNORE_LEADING_ WS = 'IGNORE_LEADING _WS'
NUMERICAL = 'NUMERICAL'
IGNORE_COMMAS = 'IGNORE_COMMAS'
PERIOD_AS_COMMA S = 'PERIOD_AS_COMM AS'

class Collate(object) :
""" A general purpose and configurable collator class.
"""
def __init__(self, flags=[]):
self.flags = flags
self.numrex = re.compile(r'([\d\.]*|\D*)', re.LOCALE)
self.txtable = []
if HYPHEN_AS_SPACE in flags:
self.txtable.ap pend(('-', ' '))
if UNDERSCORE_AS_S PACE in flags:
self.txtable.ap pend(('_', ' '))
if PERIOD_AS_COMMA S in flags:
self.txtable.ap pend(('.', ','))
if IGNORE_COMMAS in flags:
self.txtable.ap pend((',', ''))
self.flags = flags

def transform(self, s):
""" Transform a string for collating.
"""
if not self.flags:
return locale.strxfrm( s)
for a, b in self.txtable:
s = s.replace(a, b)
if IGNORE_LEADING_ WS in self.flags:
s = s.strip()
if CAPS_FIRST in self.flags:
s = s.swapcase()
if NUMERICAL in self.flags:
slist = self.numrex.spl it(s)
for i, x in enumerate(slist ):
try:
slist[i] = float(x)
except:
slist[i] = locale.strxfrm( x)
return slist
return locale.strxfrm( s)

def __call__(self, a):
""" This allows the Collate class work as a sort key.

USE: list.sort(key=C ollate(flags))
"""
return self.transform( a)

def collate(slist, flags=[]):
""" Collate list of strings in place.
"""
slist.sort(key= Collate(flags). transform)

def collated(slist, flags=[]):
""" Return a collated list of strings.
"""
return sorted(slist, key=Collate(fla gs).transform)

def _test():
"""
DOC TESTS AND EXAMPLES:

Sort (and sorted) normally order all words beginning with caps
before all words beginning with lower case.

>>t = ['tuesday', 'Tuesday', 'Monday', 'monday']
sorted(t) # regular sort

['Monday', 'Tuesday', 'monday', 'tuesday']

Locale collation puts words beginning with caps after words
beginning with lower case of the same letter.

>>collated(t)

['monday', 'Monday', 'tuesday', 'Tuesday']

The CAPS_FIRST option can be used to put all words beginning
with caps before words beginning in lowercase of the same letter.

>>collated(t, [CAPS_FIRST])

['Monday', 'monday', 'Tuesday', 'tuesday']
The HYPHEN_AS_SPACE option causes hyphens to be equal to space.

>>t = ['a-b', 'b-a', 'aa-b', 'bb-a']
collated(t)

['aa-b', 'a-b', 'b-a', 'bb-a']

>>collated(t, [HYPHEN_AS_SPACE])

['a-b', 'aa-b', 'b-a', 'bb-a']
The IGNORE_LEADING_ WS and UNDERSCORE_AS_S PACE options can be
used together to improve ordering in some situations.

>>t = ['sum', '__str__', 'about', ' round']
collated(t)

[' round', '__str__', 'about', 'sum']

>>collated(t, [IGNORE_LEADING_ WS])

['__str__', 'about', ' round', 'sum']

>>collated(t, [UNDERSCORE_AS_S PACE])

[' round', '__str__', 'about', 'sum']

>>collated(t, [IGNORE_LEADING_ WS, UNDERSCORE_AS_S PACE])

['about', ' round', '__str__', 'sum']
The NUMERICAL option orders sequences of digits as numerals.

>>t = ['a5', 'a40', '4abc', '20abc', 'a10.2', '13.5b', 'b2']
collated(t, [NUMERICAL])

['4abc', '13.5b', '20abc', 'a5', 'a10.2', 'a40', 'b2']
The IGNORE_COMMAS option prevents commas from seperating numerals.

>>t = ['a5', 'a4,000', '500b', '100,000b']
collated(t, [NUMERICAL, IGNORE_COMMAS])

['500b', '100,000b', 'a5', 'a4,000']
The PERIOD_AS_COMMA S option can be used to sort version numbers
and other decimal seperated numbers correctly.

>>t = ['5.1.1', '5.10.12','5.2. 2', '5.2.19' ]
collated(t, [NUMERICAL, PERIOD_AS_COMMA S])

['5.1.1', '5.2.2', '5.2.19', '5.10.12']

Collate also can be done in place by using collate() instead of
collated().

>>t = ['Fred', 'Ron', 'Carol', 'Bob']
collate(t)
t

['Bob', 'Carol', 'Fred', 'Ron']

"""
import doctest
doctest.testmod ()
if __name__ == '__main__':
_test()

[Ron Adam]

Thanks, But I fixed it already. (almost) ;-)

I think I will use strings as you suggest, and verify they are valid so a type
don't go though silently.

I ended up using string based option list. I agree a space separated string is
better and easier from a user point of view.

The advantage of the list is it can be iterated without splitting first. But
that's a minor thing. self.options = options.lower() .split(' ') fixes that easily.
Once I'm sure it's not going to get any major changes I'll post this as a
recipe. I think it's almost there.

Cheers and thanks,
Ron

be************@ lycos.com wrote:

This part of code uses integer "constants" to be or-ed (or added):

CAPS_FIRST = 1
NUMERICAL = 2
HYPHEN_AS_SPACE = 4
UNDERSCORE_AS_S PACE = 8
IGNORE_LEADING_ WS = 16
COMMA_IN_NUMERA LS = 32

...

def __init__(self, flag):
self.flag = flag
def transform(self, s):
""" Transform a string for collating.
"""
if self.flag & CAPS_FIRST:
s = s.swapcase()
if self.flag & HYPHEN_AS_SPACE :
s = s.replace('-', ' ')
if self.flag & UNDERSCORE_AS_S PACE:
s = s.replace('_', ' ')
if self.flag & IGNORE_LEADING_ WS:
s = s.strip()
if self.flag & NUMERICAL:
if self.flag & COMMA_IN_NUMERA LS:

This is used in C, but maybe for Python other solutions may be better.
I can see some different (untested) solutions:

1)

def selfassign(self , locals):
# Code from web.py, modified.
for key, value in locals.iteritem s():
if key != 'self':
setattr(self, key, value)

def __init__(self,
caps_first=Fals e,
hyphen_as_space =False,
underscore_as_s pace=False,
ignore_leading_ ws=False,
numerical=False ,
comma_in_numera ls=False):
selfassign(self , locals())

def transform(self, s):
if self.caps_first :
...

Disadvangages: if a flag is added/modified, the code has to be modified
in two places.
2)

def __init__(self, **kwds):
self.lflags = [k for k,v in kwds.items() if v]
def transform(self, s):
if "caps_first " in self.lflags:
...

This class can be created with 1 instead of Trues, to shorten the code.

Disadvantages: the user of this class has to read from the class
doctring or from from the docs the list of possible flags (and such
docs can be out of sync from the code).
3)

Tkinter (Tcl) shows that sometimes strings are better than int
constants (like using "left" instead of tkinter.LEFT, etc), so this is
another possibile solution:

I think maybe this is better, but I need to verify the flags so typos don't go
though silently.

def __init__(self, flags=""):
self.lflags = flags.lower().s plit()
def transform(self, s):
if "caps_first " in self.lflags:
...

An example of calling this class:

... = Collate("caps_f irst hyphen_as_space numerical")

I like this third (nonstandard) solution enough.

Bye,
bearophile

[Ron Adam]

This is how I changed it...

(I edited out the test and imports for posting here.)

locale.setlocal e(locale.LC_ALL , '') # use current locale settings

class Collate(object) :
""" A general purpose and configurable collator class.
"""
options = [ 'CAPS_FIRST', 'NUMERICAL', 'HYPHEN_AS_SPAC E',
'UNDERSCORE_AS_ SPACE', 'IGNORE_LEADING _WS',
'IGNORE_COMMAS' , 'PERIOD_AS_COMM AS' ]

def __init__(self, flags=""):
if flags:
flags = flags.upper().s plit()
for value in flags:
if value not in self.options:
raise ValueError, 'Invalid option: %s' % value
self.txtable = []
if 'HYPHEN_AS_SPAC E' in flags:
self.txtable.ap pend(('-', ' '))
if 'UNDERSCORE_AS_ SPACE' in flags:
self.txtable.ap pend(('_', ' '))
if 'PERIOD_AS_COMM AS' in flags:
self.txtable.ap pend(('.', ','))
if 'IGNORE_COMMAS' in flags:
self.txtable.ap pend((',', ''))
self.flags = flags
self.numrex = re.compile(r'([\d\.]*|\D*)', re.LOCALE)

def transform(self, s):
""" Transform a string for collating.
"""
if not self.flags:
return locale.strxfrm( s)
for a, b in self.txtable:
s = s.replace(a, b)
if 'IGNORE_LEADING _WS' in self.flags:
s = s.strip()
if 'CAPS_FIRST' in self.flags:
s = s.swapcase()
if 'NUMERICAL' in self.flags:
slist = self.numrex.spl it(s)
for i, x in enumerate(slist ):
try:
slist[i] = float(x)
except:
slist[i] = locale.strxfrm( x)
return slist
return locale.strxfrm( s)

def __call__(self, a):
""" This allows the Collate class to be used as a sort key.

USE: list.sort(key=C ollate(flags))
"""
return self.transform( a)

def collate(slist, flags=[]):
""" Collate list of strings in place.
"""
slist.sort(key= Collate(flags). transform)

def collated(slist, flags=[]):
""" Return a collated list of strings.
"""
return sorted(slist, key=Collate(fla gs).transform)

[bearophileHUGS]

Ron Adam:

Insted of:

def __init__(self, flags=[]):
self.flags = flags
self.numrex = re.compile(r'([\d\.]*|\D*)', re.LOCALE)
self.txtable = []
if HYPHEN_AS_SPACE in flags:
self.txtable.ap pend(('-', ' '))
if UNDERSCORE_AS_S PACE in flags:
self.txtable.ap pend(('_', ' '))
if PERIOD_AS_COMMA S in flags:
self.txtable.ap pend(('.', ','))
if IGNORE_COMMAS in flags:
self.txtable.ap pend((',', ''))
self.flags = flags

I think using a not mutable flags default is safer, this is an
alternative (NOT tested!):

numrex = re.compile(r'[\d\.]* | \D*', re.LOCALE|re.VE RBOSE)
dflags = {"hyphen_as_spa ce": ('-', ' '),
"underscore_as_ space": ('_', ' '),
"period_as_comm as": ('_', ' '),
"ignore_commas" : (',', ''),
...
}

def __init__(self, flags=()):
self.flags = [fl.strip().lowe r() for fl in flags]
self.txtable = []
df = self.__class__. dflags
for flag in self.flags:
if flag in df:
self.txtable.ap pend(df[flag])
...

This is just an idea, it surely has some problems that have to be
fixed.

Bye,
bearophile

[Gabriel Genellina]

At Wednesday 18/10/2006 03:42, Ron Adam wrote:

>I put together the following module today and would like some feedback on any
obvious problems. Or even opinions of weather or not it is a good approach.
if self.flag & CAPS_FIRST:
s = s.swapcase()

This is just coincidental; it relies on (lowercase)<(up percase) on
the locale collating sequence, and I don't see why it should be always so.

if self.flag & IGNORE_LEADING_ WS:
s = s.strip()

This ignores trailing ws too. (lstrip?)

if self.flag & NUMERICAL:
if self.flag & COMMA_IN_NUMERA LS:
rex =
re.compile('^(\ d*\,?\d*\.?\d*) (\D*)(\d*\,?\d* \.?\d*)',
re.LOCALE)
else:
rex = re.compile('^(\ d*\.?\d*)(\D*)( \d*\.?\d*)', re.LOCALE)
slist = rex.split(s)
for i, x in enumerate(slist ):
if self.flag & COMMA_IN_NUMERA LS:
x = x.replace(',', '')
try:
slist[i] = float(x)
except:
slist[i] = locale.strxfrm( x)
return slist
return locale.strxfrm( s)

You should try to make this part a bit more generic. If you are
concerned about locales, do not use "comma" explicitely. In other
countries 10*100=1.000 - and 1,234 is a fraction between 1 and 2.

The NUMERICAL option orders leading and trailing digits as numerals.

>>t = ['a5', 'a40', '4abc', '20abc', 'a10.2', '13.5b', 'b2']
>>collated(t, NUMERICAL)

['4abc', '13.5b', '20abc', 'a5', 'a10.2', 'a40', 'b2']

From the name "NUMERICAL" I would expect this sorting: b2, 4abc, a5,
a10.2, 13.5b, 20abc, a40 (that is, sorting as numbers only).
Maybe GROUP_NUMBERS.. . but I dont like that too much either...
--
Gabriel Genellina
Softlab SRL

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