Detecting consecutive integers in a list

Question

I have a list containing data as such:

[1, 2, 3, 4, 7, 8, 10, 11, 12, 13, 14]

I'd like to print out the ranges of consecutive integers:

1-4, 7-8, 10-14

Is there a built-in/fast/efficient way of doing this?

Answer 1

From the docs:

>>> data = [ 1, 4,5,6, 10, 15,16,17,18, 22, 25,26,27,28]
>>> for k, g in groupby(enumerate(data), lambda (i,x):i-x):
...     print map(itemgetter(1), g)
...
[1]
[4, 5, 6]
[10]
[15, 16, 17, 18]
[22]
[25, 26, 27, 28]

You can adapt this fairly easily to get a printed set of ranges.

Answer 2

Built-In: No, as far as I'm aware.

You have to run through the array. Start off with putting the first value in a variable and print it, then as long as you keep hitting the next number do nothing but remember the last number in another variable. If the next number is not in line, check the last number remembered versus the first number. If it's the same, do nothing. If it's different, print "-" and the last number. Then put the current value in the first variable and start over. At the end of the array you run the same routine as if you had hit a number out of line.

I could have written the code, of course, but I don't want to spoil your homework :-)