消去Python中list的重复元素

原文地址：http://www.peterbe.com/plog/uniqifiers-benchmark

Fastest way to uniqify a list in Python

Suppose you have a list in python that looks like this:

[ 'a' , 'b' , 'a' ]
#orlikethis:
[ 1 , 2 , 2 , 2 , 3 , 4 , 5 , 6 , 6 , 6 , 6 ]

and you want to remove all duplicates so you get this result:

[ 'a' , 'b' ]
#or
[ 1 , 2 , 3 , 4 , 5 , 6 ]

from random import shuffle, randint import re from sets import Set def f1(seq): # Raymond Hettinger # not order preserving set = {} map(set.__setitem__, seq, []) return set.keys() def f2(seq): # ********* # order preserving checked = [] for e in seq: if e not in checked: checked.append(e) return checked def f3(seq): # Not order preserving keys = {} for e in seq: keys[e] = 1 return keys.keys() def f4(seq): # ********** order preserving noDupes = [] [noDupes.append(i) for i in seq if not noDupes.count(i)] return noDupes def f5(seq, idfun=None): # Alex Martelli ******* order preserving if idfun is None: def idfun(x): return x seen = {} result = [] for item in seq: marker = idfun(item) # in old Python versions: # if seen.has_key(marker) # but in new ones: if marker in seen: continue seen[marker] = 1 result.append(item) return result def f5b(seq, idfun=None): # Alex Martelli ******* order preserving if idfun is None: def idfun(x): return x seen = {} result = [] for item in seq: marker = idfun(item) # in old Python versions: # if seen.has_key(marker) # but in new ones: if marker not in seen: seen[marker] = 1 result.append(item) return result def f6(seq): # Not order preserving return list(Set(seq)) def f7(seq): # Not order preserving return list(set(seq)) def f8(seq): # Dave Kirby # Order preserving seen = set() return [x for x in seq if x not in seen and not seen.add(x)] def f9(seq): # Not order preserving return {}.fromkeys(seq).keys() def f10(seq, idfun=None): # Andrew Dalke # Order preserving return list(_f10(seq, idfun)) def _f10(seq, idfun=None): seen = set() if idfun is None: for x in seq: if x in seen: continue seen.add(x) yield x else: for x in seq: x = idfun(x) if x in seen: continue seen.add(x) yield x def f11(seq): # f10 but simpler # Order preserving return list(_f10(seq)) def _f11(seq): seen = set() for x in seq: if x in seen: continue seen.add(x) yield x import time def timing(f, n, a): print f.__name__, r = range(n) t1 = time.clock() for i in r: f(a); f(a); f(a); f(a); f(a); f(a); f(a); f(a); f(a); f(a) t2 = time.clock() print round(t2-t1, 3) def getRandomString(length=10, loweronly=1, numbersonly=0, lettersonly=0): """ return a very random string """ _letters = 'abcdefghijklmnopqrstuvwxyz' if numbersonly: l = list('0123456789') elif lettersonly: l = list(_letters + _letters.upper()) else: lowercase = _letters+'0123456789'*2 l = list(lowercase + lowercase.upper()) shuffle(l) s = ''.join(l) if len(s) < length: s = s + getRandomString(loweronly=1) s = s[:length] if loweronly: return s.lower() else: return s testdata = {} for i in range(35): k = getRandomString(5, lettersonly=1) v = getRandomString(100 ) testdata[k] = v testdata = [int(x) for x in list('21354612')] testdata += list('abcceeaa5efm') class X: def __init__(self, n): self.foo = n def __repr__(self): return "<foo %r>"%self.foo def __cmp__(self, e): return cmp(self.foo, e.foo) testdata = [] for i in range(10000): testdata.append(getRandomString(3, loweronly=True)) #testdata = ['f','g','c','d','b','a','a'] order_preserving = f2, f4, f5, f5b, f8, f10, f11 order_preserving = f5, f5b, f8, f10, f11 not_order_preserving = f1, f3, f6, f7, f9 testfuncs = order_preserving + not_order_preserving for f in testfuncs: if f in order_preserving: print "*", timing(f, 100, testdata)