George Sakkis wrote:
On Aug 27, 3:00 pm, Gerard flanagan <[EMAIL PROTECTED]> wrote:
[EMAIL PROTECTED] wrote:
I have a list that starts with zeros, has sporadic data, and then has
good data. I define the point at which the data turns good to be the
first index with a non-zero entry that is followed by at least 4
consecutive non-zero data items (i.e. a week's worth of non-zero
data). For example, if my list is [0, 0, 1, 0, 1, 2, 3, 4, 5, 6, 7, 8,
9], I would define the point at which data turns good to be 4 (1
followed by 2, 3, 4, 5).
I have a simple algorithm to identify this changepoint, but it looks
crude: is there a cleaner, more elegant way to do this?
flag = True
i=-1
j=0
while flag and i < len(retHist)-1:
i += 1
if retHist[i] == 0:
j = 0
else:
j += 1
if j == 5:
flag = False
del retHist[:i-4]
Thanks in advance for your help
Thomas Philips
data = [0, 0, 1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
def itergood(indata):
indata = iter(indata)
buf = []
while len(buf) < 4:
buf.append(indata.next())
if buf[-1] == 0:
buf[:] = []
for x in buf:
yield x
for x in indata:
yield x
for d in itergood(data):
print d
This seems the most efficient so far for arbitrary iterables. With a
few micro-optimizations it becomes:
from itertools import chain
def itergood(indata, good_ones=4):
indata = iter(indata); get_next = indata.next
buf = []; append = buf.append
while len(buf) < good_ones:
next = get_next()
if next: append(next)
else: del buf[:]
return chain(buf, indata)
$ python -m timeit -s "x = 1000*[0, 0, 0, 1, 2, 3] + [1,2,3,4]; from
itergood import itergood" "list(itergood(x))"
100 loops, best of 3: 3.09 msec per loop
And with Psyco enabled:
$ python -m timeit -s "x = 1000*[0, 0, 0, 1, 2, 3] + [1,2,3,4]; from
itergood import itergood" "list(itergood(x))"
1000 loops, best of 3: 466 usec per loop
George
--
I always forget the 'del slice' method for clearing a list, thanks.
I think that returning a `chain` means that the function is not itself a
generator. And so if the indata has length less than or equal
to the threshold (good_ones), an unhandled StopIteration is raised
before the return statement is reached.
G.
--
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