mirror of
https://github.com/Sneed-Group/Poodletooth-iLand
synced 2024-12-25 12:42:41 -06:00
203 lines
8 KiB
Python
203 lines
8 KiB
Python
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from itertools import tee
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def itersorted(iterable, cmp = cmp, key = lambda x: x, reverse = False):
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"""
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This function returns a generator object that yields sorted items from
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'iterable'.
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It implements a form of lazy sorting that's most useful in two cases:
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1) When you only need the first few values in the sorted data.
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2) When you want to amortize the cost of the sort over the time
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you use the data.
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It is to be considered a 'stable sort', where values with equivalent
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sorting criteria maintain their relative order as it is in the input
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data set.
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'cmp' MUST return values in [-1,0,1]. Otherwise, behavior is
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undefined, and will most likely be very incorrect.
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"""
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# Notes:
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# Understanding the concepts of 'left' and 'right' here is important.
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# 'left' values are those that are yielded earlier in the sort. So
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# each subsequent value yielded is 'to the right' of the previous one.
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# A stack is used to maintain sets of values who share the same key
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# value. Each layer corresponds to one key. During the traversals of
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# the input data, values are added to each layer in such a way that
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# they maintain their relative position (to others in the same layer)
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# from the original data. This ensures a 'stable sort'.
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# Create our working structures
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stack = [] # holds a stack of 'layers'.
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# 'left' value layers are above 'right' ones.
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layer = () # A 3-tuple of the form:
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# (key, data iterator, [values])
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init = True # Is set to true for the first pass through
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# the data.
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if reverse: # Use this to easily switch the direction of the sort.
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rev = -1
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else:
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rev = 1
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# Create the base iterator that will track our
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# main progress through the data.
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a = ((key(x),x) for x in iterable)
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# Begin the main loop
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while 1:
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# If the stack is empty, we must now seed it.
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# Advance the base iterator until we find a value 'to the right' of
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# anything we've yielded so far. (All values 'to the left' have
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# already been yielded)
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if not stack:
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# pull next value off the base iterator
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k,val = a.next()
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# If init, get the first value and stop.
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# Otherwise, find the first value 'to the right'
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# of the most recently yielded value.
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while (not init) and (cmp(k,lLimit) != rev):
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k,val = a.next()
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pass
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# Place the found value as the initial stack value
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# (and store its iteration progress as well).
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a,b = tee(a)
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stack.append([k, b, [val]])
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pass
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# We now iterate through the data, starting where the value
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# at the top of the stack left off.
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layer = stack[-1]
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b = layer[1]
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for k,val in b:
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# If the next data element is 'to the left' of (or equal to)
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# the top off the stack and 'to the right' of the last element
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# yielded, add it to the stack.
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if cmp(k,layer[0]) != rev and (init or cmp(k,lLimit) == rev):
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# If it's 'to the left' of the current stack value,
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# make a new layer and add it to the top of the stack.
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# Otherwise, it's equivalent so we'll just append it
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# to the values in the top layer of the stack.
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if cmp(k,layer[0]) == -rev:
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b,layer[1] = tee(b)
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stack.append([k, b, []])
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layer = stack[-1]
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pass
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layer[2].append(val)
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pass
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pass
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# Remove the initialization condition to enable lLimit checking.
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init = False
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# Whatever values that are on the top stack at this point are
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# the 'left-most' we've found that we haven't yet yielded. Yield
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# them in the order that we discovered them in the source data.
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# Define lLimit as the right-most limit for values that have not
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# yet been yielded. This will allow us to ignore these values
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# on future iterations.
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lLimit, b, vals = stack.pop()
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for val in vals:
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yield val
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pass
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if __debug__:
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def P(i):
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for x in reversed(i):
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print x
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def test():
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import random
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from itertools import islice
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control = sorted(data, key = lambda x: x[0])
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variable = itersorted(data, key = lambda x: x[0])
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print control[:10] == [x for x in islice(variable,10)]
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print data
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print control
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variable = itersorted(data, key = lambda x: x[0])
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print [x for x in islice(variable,10)]
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from unittest import TestCase, main
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from random import shuffle
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from itertools import islice
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class LazySortTest(TestCase):
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"""
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Run these tests with:
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> python LazySort.py
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"""
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TESTLEN = 10
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RANGELEN = max(TESTLEN, 10)
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a = range(RANGELEN/2)*2
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b = range(RANGELEN/2)*2
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shuffle(a)
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shuffle(b)
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DATA = zip(a,b)
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shuffle(DATA)
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del a
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del b
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def testRange(self):
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control = sorted(self.DATA)
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variable = itersorted(self.DATA)
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeCompare(self):
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control = sorted(self.DATA, cmp = lambda a,b: -cmp(a,b))
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variable = itersorted(self.DATA, cmp = lambda a,b: -cmp(a,b))
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeKey(self):
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control = sorted(self.DATA, key = lambda x: x[0])
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variable = itersorted(self.DATA, key = lambda x: x[0])
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeReverse(self):
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control = sorted(self.DATA, reverse = True)
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variable = itersorted(self.DATA, reverse = True)
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeCompareKey(self):
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control = sorted(self.DATA, cmp = lambda a,b: -cmp(a,b),
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key = lambda x: x[0])
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variable = itersorted(self.DATA, cmp = lambda a,b: -cmp(a,b),
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key = lambda x: x[0])
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeCompareReverse(self):
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control = sorted(self.DATA, cmp = lambda a,b: -cmp(a,b),
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reverse = True)
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variable = itersorted(self.DATA, cmp = lambda a,b: -cmp(a,b),
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reverse = True)
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeKeyReverse(self):
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control = sorted(self.DATA, key = lambda x: x[0], reverse = True)
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variable = itersorted(self.DATA, key = lambda x: x[0], reverse = True)
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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control = sorted(self.DATA, key = lambda x: x[1], reverse = True)
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variable = itersorted(self.DATA, key = lambda x: x[1], reverse = True)
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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def testRangeCompareKeyReverse(self):
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control = sorted(self.DATA, cmp = lambda a,b: -cmp(a,b),
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key = lambda x: x[0],
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reverse = True)
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variable = itersorted(self.DATA, cmp = lambda a,b: -cmp(a,b),
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key = lambda x: x[0],
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reverse = True)
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self.assertEqual(control[:10], [x for x in islice(variable, self.TESTLEN)])
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if __name__ == '__main__':
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main() # unittest.main
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