我想从列表中删除一个值,如果它存在于列表中(它可能不存在)。
a = [1, 2, 3, 4]
b = a.index(6)
del a[b]
print(a)
上面给出了错误:
ValueError: list.index(x): x not in list
所以我必须这样做:
a = [1, 2, 3, 4]
try:
b = a.index(6)
del a[b]
except:
pass
print(a)
难道没有更简单的方法吗?
我想从列表中删除一个值,如果它存在于列表中(它可能不存在)。
a = [1, 2, 3, 4]
b = a.index(6)
del a[b]
print(a)
上面给出了错误:
ValueError: list.index(x): x not in list
所以我必须这样做:
a = [1, 2, 3, 4]
try:
b = a.index(6)
del a[b]
except:
pass
print(a)
难道没有更简单的方法吗?
当前回答
要删除一个元素的第一次出现,使用list.remove:
>>> xs = ['a', 'b', 'c', 'd']
>>> xs.remove('b')
>>> print(xs)
['a', 'c', 'd']
要移除所有出现的元素,使用列表推导式:
>>> xs = ['a', 'b', 'c', 'd', 'b', 'b', 'b', 'b']
>>> xs = [x for x in xs if x != 'b']
>>> print(xs)
['a', 'c', 'd']
其他回答
使用一个for循环和一个条件:
def cleaner(seq, value):
temp = []
for number in seq:
if number != value:
temp.append(number)
return temp
如果你想删除一些,但不是全部:
def cleaner(seq, value, occ):
temp = []
for number in seq:
if number == value and occ:
occ -= 1
continue
else:
temp.append(number)
return temp
如果你知道要删除什么值,这里有一个简单的方法(就像我能想到的一样简单):
a = [0, 1, 1, 0, 1, 2, 1, 3, 1, 4]
while a.count(1) > 0:
a.remove(1)
你会得到 [0,0,2,3,4]
一些最简单的基准测试方法:
import random
from copy import copy
sample = random.sample(range(100000), 10000)
remove = random.sample(range(100000), 1000)
%%timeit
sample1 = copy(sample)
remove1 = copy(remove)
for i in reversed(sample1):
if i in remove1:
sample1.remove(i)
# 271 ms ± 16 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# remove all instances
%%timeit
sample1 = copy(sample)
remove1 = copy(remove)
filtered = list(filter(lambda x: x not in remove1, sample1))
# 280 ms ± 18.9 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# remove all instances
%%timeit
sample1 = copy(sample)
remove1 = copy(remove)
filtered = [ele for ele in sample1 if ele not in remove1]
# 293 ms ± 72.1 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# remove all instances
%%timeit
sample1 = copy(sample)
remove1 = copy(remove)
for val in remove1:
if val in sample1:
sample1.remove(val)
# 558 ms ± 40.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# only remove first occurrence
%%timeit
sample1 = copy(sample)
remove1 = copy(remove)
for val in remove1:
try:
sample1.remove(val)
except:
pass
# 609 ms ± 11.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
# only remove first occurrence
这是一个效率较低的解决方案,但它仍然有效:
A =[] //这是你的列表
B //需要删除的元素
counter = a.count(b)
while counter > 0:
if b in a:
a.remove(b)
counter -= 1
print(a)
例如,我们想要从x中移除所有的1,我是这样做的:
x = [1, 2, 3, 1, 2, 3]
这是我的方法的一个实际应用:
def Function(List, Unwanted):
[List.remove(Unwanted) for Item in range(List.count(Unwanted))]
return List
x = Function(x, 1)
print(x)
这是我的方法,只用一行:
[x.remove(1) for Item in range(x.count(1))]
print(x)
两者的输出都是:
[2, 3, 2, 3, 2, 3]
希望这能有所帮助。 PS,请注意这是在3.6.2版本中编写的,所以您可能需要针对旧版本进行调整。