I'd like to know if there is a simple (or already created) way of doing the opposite of this: Generate List of Numbers from Hyphenated.... This link could be used to do:
>> list(hyphen_range('1-9,12,15-20,23'))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 15, 16, 17, 18, 19, 20, 23]:
I'm looking to do the opposite (note that 10 and 21 are included so it would be compatible with the range function, where range(1,10)=[1,2,3,4,5,6,7,8,9]):
>> list_to_ranges([1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 15, 16, 17, 18, 19, 20, 23])
'1-10,12,15-21,23'
Eventually, I would like to have the output also incorporate a step where the last number of the output indicates the step:
>> list_to_ranges([1, 3, 5, 7, 8, 9, 10, 11])
'1-13:2,8,10'
Essentially, this would end up being kind of like an "inverse" range function
>> tmp = list_to_ranges([1, 3, 5])
>> print tmp
'1-7:2'
>> range(1, 7, 2)
[1, 3, 5]
My guess is that there is no really easy/simple way to do this, but I thought I would ask on here before I go make some brute force, long method.
EDIT
Using the code from an answer to this post as an example, I came up with a simple way to do the first part. But I think that identifying the patterns to do steps would be a bit harder.
from itertools import groupby
from operator import itemgetter
data = [ 1, 4,5,6, 10, 15,16,17,18, 22, 25,26,27,28]
print data, '\n'
str_list = []
for k, g in groupby(enumerate(data), lambda (i,x):i-x):
ilist = map(itemgetter(1), g)
print ilist
if len(ilist) > 1:
str_list.append('%d-%d' % (ilist[0], ilist[-1]+1))
else:
str_list.append('%d' % ilist[0])
print '\n', ','.join(str_list)
EDIT 2
Here is my attempt at including the step size...it is pretty close, but the first numbers get repeated. I think that with a little bit of tweaking of this, it will be close to what I want - or at least good enough.
import numpy as np
from itertools import groupby
def list_to_ranges(data):
data = sorted(data)
diff_data = np.diff(data).tolist()
ranges = []
i = 0
for k, iterable in groupby(diff_data, None):
rng = list(iterable)
step = rng[0]
if len(rng) == 1:
ranges.append('%d' % data[i])
elif step == 1:
ranges.append('%d-%d' % (data[i], data[i+len(rng)]+step))
else:
ranges.append('%d-%d:%d' % (data[i], data[i+len(rng)]+step, step))
i += len(rng)
return ','.join(ranges)
data = [1, 3, 5, 6, 7, 11, 13, 15, 16, 17, 18, 19, 22, 25, 28]
print data
data_str = list_to_ranges(data)
print data_str
_list = []
for r in data_str.replace('-',':').split(','):
r = [int(a) for a in r.split(':')]
if len(r) == 1:
_list.extend(r)
elif len(r) == 2:
_list.extend(range(r[0], r[1]))
else:
_list.extend(range(r[0], r[1], r[2]))
print _list
print list(set(_list))
One approach could be "eating" piece by piece the input sequence and store the partial range results untill you've got them all:
def formatter(start, end, step):
return '{}-{}:{}'.format(start, end, step)
# return '{}-{}:{}'.format(start, end + step, step)
def helper(lst):
if len(lst) == 1:
return str(lst[0]), []
if len(lst) == 2:
return ','.join(map(str,lst)), []
step = lst[1] - lst[0]
for i,x,y in zip(itertools.count(1), lst[1:], lst[2:]):
if y-x != step:
if i > 1:
return formatter(lst[0], lst[i], step), lst[i+1:]
else:
return str(lst[0]), lst[1:]
return formatter(lst[0], lst[-1], step), []
def re_range(lst):
result = []
while lst:
partial,lst = helper(lst)
result.append(partial)
return ','.join(result)
I test it with a bunch of unit tests and it passed them all, it can handle negative numbers too, but they'll look kind of ugly (it's really anybody's fault).
Example:
>>> re_range([1, 4,5,6, 10, 15,16,17,18, 22, 25,26,27,28])
'1,4-6:1,10,15-18:1,22,25-28:1'
>>> re_range([1, 3, 5, 7, 8, 9, 10, 11, 13, 15, 17])
'1-7:2,8-11:1,13-17:2'
Note: I wrote the code for Python 3.
I didn't put any performance effort in the solution above. In particular, every time a list get re-builded with slicing, it might take some time if the input list has a particular shape. So, the first simple improvement would be using itertools.islice() where possible.
Anyway here's another implementation of the same algorithm, that scan through the input list with a scan index instead of slicing:
def re_range(lst):
n = len(lst)
result = []
scan = 0
while n - scan > 2:
step = lst[scan + 1] - lst[scan]
if lst[scan + 2] - lst[scan + 1] != step:
result.append(str(lst[scan]))
scan += 1
continue
for j in range(scan+2, n-1):
if lst[j+1] - lst[j] != step:
result.append(formatter(lst[scan], lst[j], step))
scan = j+1
break
else:
result.append(formatter(lst[scan], lst[-1], step))
return ','.join(result)
if n - scan == 1:
result.append(str(lst[scan]))
elif n - scan == 2:
result.append(','.join(map(str, lst[scan:])))
return ','.join(result)
I stopped working on it once it got ~65% faster than the previous top solution, it seemed enough :)
Anyway I'd say that there might still be room for improvement (expecially in the middle for-loop).