我需要一个函数,它接受一个列表并输出True,如果输入列表中的所有元素使用标准相等运算符计算彼此相等,否则输出False。

我觉得最好是遍历列表,比较相邻的元素,然后与所有结果布尔值。但我不知道最python的方法是什么。


当前回答

您可以使用.nunique()来查找列表中唯一项的数量。

def identical_elements(list):
    series = pd.Series(list)
    if series.nunique() == 1: identical = True
    else:  identical = False
    return identical



identical_elements(['a', 'a'])
Out[427]: True

identical_elements(['a', 'b'])
Out[428]: False

其他回答

这是一种简单的方法:

result = mylist and all(mylist[0] == elem for elem in mylist)

这稍微复杂一点,它会引起函数调用开销,但语义更清楚地说明:

def all_identical(seq):
    if not seq:
        # empty list is False.
        return False
    first = seq[0]
    return all(first == elem for elem in seq)

这是一段具有良好的Python性的代码,并且平衡了简单性和明显性,我认为,这应该也适用于相当老的Python版本。

def all_eq(lst):
    for idx, itm in enumerate(lst):
        if not idx:   # == 0
            prev = itm
        if itm != prev:
            return False
        prev = itm
    return True

简单的解决方案是应用set on list

如果所有元素都相同,len将为1,否则大于1

lst = [1,1,1,1,1,1,1,1,1]
len_lst = len(list(set(lst)))

print(len_lst)

1


lst = [1,2,1,1,1,1,1,1,1]
len_lst = len(list(set(lst)))
print(len_lst)

2

还有一个纯Python递归选项:

def checkEqual(lst):
    if len(lst)==2 :
        return lst[0]==lst[1]
    else:
        return lst[0]==lst[1] and checkEqual(lst[1:])

然而,由于某些原因,它在某些情况下比其他选项慢两个数量级。从C语言的角度来看,我希望这更快,但事实并非如此!

另一个缺点是Python中有递归限制,在这种情况下需要进行调整。比如用这个。

最佳答案

Twitter上有一个不错的帖子,介绍了实现all_equal()函数的各种方法。

给定一个列表输入,最好的提交是:

 t.count(t[0]) == len(t)  

其他方法

下面是线程的结果:

Have groupby() compare adjacent entries. This has an early-out for a mismatch, does not use extra memory, and it runs at C speed. g = itertools.groupby(s) next(g, True) and not next(g, False) Compare two slices offset from one another by one position. This uses extra memory but runs at C speed. s[1:] == s[:-1] Iterator version of slice comparison. It runs at C speed and does not use extra memory; however, the eq calls are expensive. all(map(operator.eq, s, itertools.islice(s, 1, None))) Compare the lowest and highest values. This runs at C speed, doesn't use extra memory, but does cost two inequality tests per datum. min(s) == max(s) # s must be non-empty Build a set. This runs at C speed and uses little extra memory but requires hashability and does not have an early-out. len(set(t))==1. At great cost, this handles NaNs and other objects with exotic equality relations. all(itertools.starmap(eq, itertools.product(s, repeat=2))) Pull out the first element and compare all the others to it, stopping at the first mismatch. Only disadvantage is that this doesn't run at C speed. it = iter(s) a = next(it, None) return all(a == b for b in it) Just count the first element. This is fast, simple, elegant. It runs at C speed, requires no additional memory, uses only equality tests, and makes only a single pass over the data. t.count(t[0]) == len(t)