Python学习入门(11)——排序
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Python的内置dictionary数据类型是无序的,通过key来获取对应的value。
可是有时我们需要对dictionary中 的item进行排序输出,可能根据key,也可能根据value来排。
数组排序前后:
old_array = ['mimvp', 'mimji', 'mimgu'] new_array = sorted(old_array); # 排序后,需要赋值 print json.dump(new_array)
示例:
#/usr/bin/python # # it-homer in 2013 def test_sort(): d = {"a":"it", "b":"homer", "c":"sunboy", "d":2050} print(d) # {'a': 'it', 'c': 'sunboy', 'b': 'homer', 'd': 2050} d['h'] = "ithomer" print(d) # {'a': 'it', 'h': 'ithomer', 'c': 'sunboy', 'b': 'homer', 'd': 2050} del(d['h']) print(d) # {'a': 'it', 'c': 'sunboy', 'b': 'homer', 'd': 2050} # 字典的遍历 for k in d: print "dict[%s] = " % k, d[k] # for k in d: print("dict[%s] = %s" % (k, d[k])) # items() 遍历 for k,v in d.items(): print("dict[%s] = %s" % (k, v)) # iteritems() 遍历 for k,v in d.iteritems(): print("dict[%s] = %s" % (k, v)) # zip() 遍历 for k,v in zip(d.iterkeys(), d.itervalues()): print("dict[%s] = %s" % (k, v)) # d.keys() 遍历 for k in d.keys(): print("dict[%s] = %s" % (k, d[k])) ''' dict[a] = it dict[c][/c] = sunboy dict[b] = homer dict[d] = 2050 ''' def test_sort2(): d = {"a":("it","homer"), "b":{"e":"blog", "f":"forum"}, "c":["sun", "boy", 2050]} print(d) # {'a': ('it', 'homer'), 'c': ['sun', 'boy', 2050], 'b': {'e': 'blog', 'f': 'forum'}} print(d['a']) # ('it', 'homer') print(d['a'][0]) # it print(d['b']) # {'e': 'blog', 'f': 'forum'} print(d['b']['e']) # blog print(d['c']) # ['sun', 'boy', 2050] print(d['c'][1]) # boy d2 = d['b'] for k in d2: print("%s : %s" % (k, d2[k])) # e : blog "\n" f : forum # 字典的更新 d = {"a":"it", "b":"homer"} f = {"a":"blog", "c":"forum"} d.update(f) print d # {'a': 'blog', 'c': 'forum', 'b': 'homer'} d = {} d.setdefault("a") print d # {'a': None} d.setdefault("b", 0) print d # {'a': None, 'b': 0} import copy def test_sort3(): d = {"a":"it", "b":"homer", "c":"blog", "d":"forum"} # 字典的浅拷贝 f = d.copy() print f # {'a': 'it', 'c': 'blog', 'b': 'homer', 'd': 'forum'} # 字典的浅拷贝 d = {"a":"it", "b":"homer", "x":{"c":"blog", "d":"forum"}} print d # {'a': 'it', 'x': {'c': 'blog', 'd': 'forum'}, 'b': 'homer'} f = d.copy() print f # {'a': 'it', 'x': {'c': 'blog', 'd': 'forum'}, 'b': 'homer'} d['x']['c'] = 'change' print d # {'a': 'it', 'x': {'c': 'change', 'd': 'forum'}, 'b': 'homer'} print f # {'a': 'it', 'x': {'c': 'change', 'd': 'forum'}, 'b': 'homer'} # 字典的深拷贝 d = {"a":"it", "b":"homer", "x":{"c":"blog", "d":"forum"}} print d # {'a': 'it', 'x': {'c': 'blog', 'd': 'forum'}, 'b': 'homer'} f = copy.deepcopy(d) print f # {'a': 'it', 'x': {'c': 'blog', 'd': 'forum'}, 'b': 'homer'} d['x']['c'] = 'change' print d # {'a': 'it', 'x': {'c': 'change', 'd': 'forum'}, 'b': 'homer'} print f # {'a': 'it', 'x': {'c': 'blog', 'd': 'forum'}, 'b': 'homer'} def test_sort4(): d = {"a":1, "c":7, "e":5, "d":9, "b":3} print d # {'a': 1, 'c': 7, 'b': 3, 'e': 5, 'd': 9} # 按照key排序 for k, v in sorted(d.items(), key=lambda x:x[0]): print(k,v) # ('a', 1) ('b', 3) ('c', 7) ('d', 9) ('e', 5) # 按照key排序 for k in sorted(d.keys()): print(k,d[k]) # ('a', 1) ('b', 3) ('c', 7) ('d', 9) ('e', 5) # 按照key排序 l = list(d.keys()) l.sort() for k in l: print(k,d[k]) # ('a', 1) ('b', 3) ('c', 7) ('d', 9) ('e', 5) # 按照value排序 for k, v in sorted(d.items(), key=lambda x:x[1]): print(k,v) # ('a', 1) ('b', 3) ('e', 5) ('c', 7) ('d', 9) # 按照value 逆序排序 for k, v in sorted(d.items(), key=lambda x:x[1], reverse = True): print(k,v) # ('d', 9) ('c', 7) ('e', 5) ('b', 3) ('a', 1) # 按照value 逆序排序 for k, v in sorted(d.items(), lambda x, y: cmp(x[1], y[1]), reverse = True): print(k,v) # ('d', 9) ('c', 7) ('e', 5) ('b', 3) ('a', 1) if __name__ == "__main__": test_sort() test_sort2() test_sort3() test_sort4()
python内置sorted函数的帮助文档:
sorted(...)
sorted(iterable, cmp=None, key=None, reverse=False) --> new sorted list
看了上面这么多种对dictionary排序的方法,其实它们的核心思想都一样,即把dictionary中的元素分离出来放到一个list中,对list排序,从而间接实现对dictionary的排序。这个“元素”可以是key,value或者item。
List 字段排序
python的排序函数sort,sorted在列表排序和字典排序中的应用详解和举例
python 列表list中内置了一个十分有用的排序函数sort,sorted,它可以用于列表的排序,以下是例子。
a = [5,2,1,9,6] >>> sorted(a) #将a从小到大排序,不影响a本身结构 [1, 2, 5, 6, 9] >>> sorted(a,reverse = True) #将a从大到小排序,不影响a本身结构 [9, 6, 5, 2, 1] >>> a.sort() #将a从小到大排序,影响a本身结构 >>> a [1, 2, 5, 6, 9] >>> a.sort(reverse = True) #将a从大到小排序,影响a本身结构 >>> a [9, 6, 5, 2, 1] 注意,a.sort() 已改变其结构,b = a.sort() 是错误的写法! >>> b = ['aa','BB','bb','zz','CC'] >>> sorted(b) ['BB', 'CC', 'aa', 'bb', 'zz'] #按列表中元素每个字母的ascii码从小到大排序,如果要从大到小,请用sorted(b,reverse=True)下同 >>> c =['CCC', 'bb', 'ffff', 'z'] >>> sorted(c,key=len) #按列表的元素的长度排序 ['z', 'bb', 'CCC', 'ffff'] >>> d =['CCC', 'bb', 'ffff', 'z'] >>> sorted(d,key = str.lower ) #将列表中的每个元素变为小写,再按每个元素中的每个字母的ascii码从小到大排序 ['bb', 'CCC', 'ffff', 'z'] >>> def lastchar(s): return s[-1] >>> e = ['abc','b','AAz','ef'] >>> sorted(e,key = lastchar) #自定义函数排序,lastchar为函数名,这个函数返回列表e中每个元素的最后一个字母 ['b', 'abc', 'ef', 'AAz'] #sorted(e,key=lastchar)作用就是 按列表e中每个元素的最后一个字母的ascii码从小到大排序 >>> f = [{'name':'abc','age':20},{'name':'def','age':30},{'name':'ghi','age':25}] #列表中的元素为字典 >>> def age(s): return s['age'] >>> ff = sorted(f,key = age) #自定义函数按列表f中字典的age从小到大排序 [{'age': 20, 'name': 'abc'}, {'age': 25, 'name': 'ghi'}, {'age': 30, 'name': 'def'}] >>> f2 = sorted(f,key = lambda x:x['age']) #如果觉得上面定义一个函数代码不美观,可以用lambda的形式来定义函数,效果同上
最后一行,对 数组的某一字段排序
参考推荐:
Python中的dict, list, tuple, set 实例
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