Identifying the start of good data in a list

[Scott David Daniels]

tkpmep at hotmail.com 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


Here is one that can go iterator-to-iterator:

     def started(source):
         src = iter(source)
         lead = []
         for x in src:
             if x:
                 lead.append(x)
                 if len(lead) == 5:
                     return itertools.chain(lead, src)
             else:
                 lead = []


     print list(started([0, 0, 1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]))


--Scott David Daniels
Scott.Daniels at Acm.Org