[EMAIL PROTECTED] wrote:
> Hi Michael,
>
> Thanks for a quick response, I appreciate it. I will have to get back
> to you tomorrow, as I can't check what you've given me right now. I
> presume the fact that you mention the word note in your code you have
> realised that I'm trying to search for musical sequences.
Yes, I thought that was the most likely application
I tried to
> put my problem across in the way I did, not mentioning music, so as not
> to confuse the matter. So simply put, I'm checking a list for musical
> sequences, without having any idea as to how they might be formed.
>
What I put together does not yet address the general problem. In particular,
it
looks only at groups that start at positions that are an integral multiple of
their length i.e., 3-tuples starting only at 0,3,6,9... If you really want to
look for repetition of any sequence anywhere, then you would need a small
modification to the make_groups function:
def make_groups(sequence, n, anywhere = False):
"""return groups of length n from sequence.
bool: anywhere
False: look only at positions n*i for i = 1,2,3...
True: return every (overlapping sequence) of length n
Usage:
>>> list(make_groups(s1,3))
[['a', 'b', 'c'], ['b', 'c', 'd'], ['c', 'd', 'e']]
>>> list(make_groups(s1,3,anywhere = True))
[['a', 'b', 'c'], ['b', 'c', 'b'], ['c', 'b', 'c'], ['b', 'c', 'd'],
['c', 'd', 'c'], ['d', 'c', 'd'], ['c', 'd', 'e']]
>>>
"""
length = len(sequence)
if (length % n) and not anywhere:
raise ValueError, "Sequence length %s is not multiple of %s"\
% (length, n)
for i in xrange(0, length-n+1, anywhere or n):
yield sequence[i:i+n]
and a corresponding tweak to the compare_forms:
def compare_forms(sequence, anywhere = False):
"""test whether all groups of a sequence have the same form"""
for length in (4,3,2): # look for longest match first
forms = {}
try:
for group in make_diffs(make_groups(sequence, length, anywhere)):
forms[group] = forms.get(group,0)+1
print forms
except ValueError:
# raised if the sequence is not a multiple of length
pass
>>> compare_forms(s1, anywhere = True)
{(0, 6, 0, 1): 2, (0, 1, 2, 1): 2, (0, 1, 0, 1): 2}
{(0, 1, 2): 3, (0, 1, 0): 2, (0, 6, 0): 2}
{(0, 1): 6, (0, 6): 2}
>>>
Other questions - are your search sequences really limited to 4 notes? How
long
are the pieces you are searching? Do you not need to care about note lengths,
only pitches. Are you really (as I inferred from your examples) looking only
at
a 7-tone scale etc... etc... Anyway, I'd be happy to discuss this on-list or
off.
Michael
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