Blind Anagram於 2013年4月22日星期一UTC+8下午7時58分20秒寫道: > I would be grateful for any advice people can offer on the fastest way > > to count items in a sub-sequence of a large list. > > > > I have a list of boolean values that can contain many hundreds of > > millions of elements for which I want to count the number of True values > > in a sub-sequence, one from the start up to some value (say hi). > > > > I am currently using: > > > > sieve[:hi].count(True) > > > > but I believe this may be costly because it copies a possibly large part > > of the sieve. > > > > Ideally I would like to be able to use: > > > > sieve.count(True, hi) > > > > where 'hi' sets the end of the count but this function is, sadly, not > > available for lists. > > > > The use of a bytearray with a memoryview object instead of a list solves > > this particular problem but it is not a solution for me as it creates > > more problems than it solves in other aspects of the program. > > > > Can I assume that one possible solution would be to sub-class list and > > create a C based extension to provide list.count(value, limit)? > > > > Are there any other solutions that will avoid copying a large part of > > the list?
For those problems related to a homogeneous list of numbers , please check whether the arrays in numpy can fit your needs practically or not. Sometimes I work on numbers in varied ranges, then the list and the long integers in Python is really handy. -- http://mail.python.org/mailman/listinfo/python-list