Formatting consecutive numbers

Question

I\'m trying to format a list of integers with Python and I\'m having a few difficulties achieving what I\'d like.

Input is a sorted list of Integers:

Answer 1

Not the most readable solution but gets the job done. One can first determine jumps in your data (jump = difference between two elements is greater than 1). Then you just loop through you original list and collect the respective elements and join them to a string.

import numpy as np

l = np.array([1, 2, 3, 6, 8, 9])

# find indexes of jumps in your data
l_diff = np.where(np.diff(l) > 1)[0] + 1

# add one index which makes slicing easier later on
if l_diff[0] != 0:
    l_diff = np.insert(l_diff, 0, 0)

# add all the data which are groups of consecutive values
res = []    
for ix, i in enumerate(l_diff):
    try:
        sl = l[i:l_diff[ix + 1]]
        if len(sl) > 1:
            res.append([sl[0], sl[-1]])
        else:
            res.append(sl)
    # means we reached end of l_diff
    except IndexError:
        sl = l[i:]
        if len(sl) > 1:
            res.append([sl[0], sl[-1]])
        else:
            res.append(sl)


# join the data accordingly, we first have to convert integers to strings
res = ', '.join(['-'.join(map(str, ai)) for ai in res])

Then res is

'1-3, 6, 8-9'