Tim Michelsen wrote: > Hello, > would like to ask for your help on the following issue: > What procedure can I use to detect if there's a change when iterating > over a list? > > For instance if I want to extract the years 1997 and 1998 from the table > below and save them into separate files?
A list comprehension will work for this. If data is a list of triples of (year, month, volume) then this will give you a list of the 1997 triples: data1997 = [ item for item in data if item[0]==1997 ] > How do I build the average only on the 1997-year values? Given the above data1997 list can you do this? Sum the third values and divide by the length of the list. > Or how do find out that there is three successive values 3*2 and 3*2 in > the volume column? itertools.groupby() is helpful for this. It's a bit tricky to understand though. Here is an extended example: http://personalpages.tds.net/~kent37/blog/arch_m1_2005_12.html#e69 Here is an example that shows sequences of values of length 3 or more: import itertools def key(item): return item[2] for k, g in itertools.groupby(data, key=key): g = list(g) if len(g) > 2: print k, 'occurs', len(g), 'times' > > I already tried a for-loop in connection with a last_value == current > value comparison but wasn't successful at all. If you show us what you have done so far it would be easier to make suggestions. Kent _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
