记录几种有关libsvm格式数据的list和dict用法

 #  list元素求和
 sum = reduce(lambda x,y: x+y, mylist)

 # 比较两个 lists 的元素是否完全一致
 if all(x==y for x, y in zip(X, Y))
     do something

 # 按照 key 排列字典的元素，以libsvm格式输出
 sorted(dd.keys())
 sorted_dict = [(key, dd[key]) for key in sorted(dd.keys())]
 # 以libsvm格式打印
5 print ' '.join([str(key)+':'+str(dd[key]) for key in sorted(dd.keys())])

 # 按照 value 排序字典的元素
 # 仅输出排序后的key
 sorted_key = [key for key in sorted(dd, key=dd.get, reverse=True)]
 # 仅输出排序后的字典
 sorted_dict = [(key, dd[key]) for key in sorted(dd, key=dd.get, reverse=True)]
 # 以libsvm格式打印字典
 print ' '.join([str(key)+':'+str(dd[key]) for key in sorted(dd, key=dd.get, reverse=True)])

 # get key intersection of two dictionaries
 intersect = set(dict_A.keys()) & set(dict_B.keys()) 

 # sort a list of tuple
 # 以tuple的第零个元素排序
 sorted_list = sorted(tuple_list, key=lambda x:x[0])

 # 把libsvm格式数据转换为dict对象
 mydict = {x.split(':')[0]:x.split(':')[1] for x in mylist} 

 # sort list and return index of list
 # 对list排序，返回有序元素的原始下标值
 sorted_index = sorted(range(len(list)), key=lambda k: list[k])