Peter Otten <__pete...@web.de> writes: > Ho Yeung Lee wrote: > >> from itertools import groupby >> >> testing1 = [(1,1),(2,3),(2,4),(3,5),(3,6),(4,6)] >> def isneighborlocation(lo1, lo2): >> if abs(lo1[0] - lo2[0]) == 1 or lo1[1] == lo2[1]: >> return 1 >> elif abs(lo1[1] - lo2[1]) == 1 or lo1[0] == lo2[0]: >> return 1 >> else: >> return 0 >> >> groupda = groupby(testing1, isneighborlocation) >> for key, group1 in groupda: >> print key >> for thing in group1: >> print thing >> >> expect output 3 group >> group1 [(1,1)] >> group2 [(2,3),(2,4] >> group3 [(3,5),(3,6),(4,6)] > > groupby() calculates the key value from the current item only, so there's no > "natural" way to apply it to your problem. > > Possible workarounds are to feed it pairs of neighbouring items (think > zip()) or a stateful key function. Below is an example of the latter: > > $ cat sequential_group_class.py > from itertools import groupby > > missing = object() > > class PairKey: > def __init__(self, continued): > self.prev = missing > self.continued = continued > self.key = False > > def __call__(self, item): > if self.prev is not missing and not self.continued(self.prev, item): > self.key = not self.key > self.prev = item > return self.key > > def isneighborlocation(lo1, lo2): > x1, y1 = lo1 > x2, y2 = lo2 > dx = x1 - x2 > dy = y1 - y2 > return dx*dx + dy*dy <= 1 > > items = [(1,1),(2,3),(2,4),(3,5),(3,6),(4,6)] > > for key, group in groupby(items, key=PairKey(isneighborlocation)): > print key, list(group) > > $ python sequential_group_class.py > False [(1, 1)] > True [(2, 3), (2, 4)] > False [(3, 5), (3, 6), (4, 6)]
That only works if (a) The elements in the list are already clustered on group (i.e. all elements of a group are adjacent) (b) In a group the order is such that adjacent elements are direct neigbours, i.e. their distance is at most 1. So 'groupby' is not a natural solution for this problem. -- Piet van Oostrum <pie...@vanoostrum.org> WWW: http://piet.vanoostrum.org/ PGP key: [8DAE142BE17999C4] -- https://mail.python.org/mailman/listinfo/python-list
