[英]Python: fastest way to check whether two string lists are “similar”
我有兩個固定大小的字符串列表,我想檢查兩個列表是否“相似”,如以下示例所示:
list1 = ["a", None, "c", None, "e", None]
list2 = ["a", "b", "c", "d", "e", "f"]
similar = True
for i in xrange(6):
if list1[i] is not None:
if list1[i] != list2[i]:
similar = False
break
有沒有更快的方法可以做到這一點?
更新:我剛剛使用zip
測試了一些解決方案。 因為zip
將考慮兩個列表中的所有元素,所以它們的速度並不快。 請注意,在很多情況下,兩個列表中的第一個元素是不同的,因此我提供的程序會立即停止檢查其余元素,從而提供了更快的解決方案。
如果您擔心提早退房,可以這樣做:
iter1, iter2 = iter(list1), iter(list2)
similar = True
while True: # or `while similar`
try:
a, b = next(iter1), next(iter2)
except StopIteration:
break
if a is not None and b is not None and a != b:
similar = False
break
# similar is your result
等同於:
import itertools
all(a==b for a,b in itertools.izip(list1, list2) if a is not None and b is not None)
等同於:
import itertools
for a,b in itertools.izip(list1, list2):
if a is None or b is None:
continue
if a != b:
break
else:
# similar
有沒有更快的方法可以做到這一點?
是的,擺脫if
嵌套會有所不同:
list1 = ["a", None, "c", None, "e", None]
list2 = ["a", "b", "c", "d", "e", "f"]
similar = True
for i in xrange(6):
if list1[i] is not None and list1[i] != list2[i]:
similar = False
break
print(similar)
# True
我認為這個算法是錯誤的。 如果list1
和list2
互換:
list1, list2 = list2, list1
similar = True
for i in xrange(6):
if list1[i] is not None and list1[i] != list2[i]:
similar = False
break
print(similar)
# False
但是它們是兩個相同的列表,仍應視為相似。 IMO此代碼(在兩個列表中均檢查“ None
是正確的:
similar = True
for i in xrange(6):
if ((list1[i] is not None and list2[i] is not None) and
list1[i] != list2[i]):
similar = False
break
print(similar)
# True
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