Python比较两个不同长度的列表

Question

您好，我想比较两个不同长度的列表，并打印一个排序表，其中包含每个表中缺少的项目。我部分能够完成此操作并打印 list_2 中缺少的值。但我也无法从 list_2 中打印 list_1 中缺少的值，即字母“z”。如何执行此操作以获得以下所需的输出？

list_1 = ['a', 'b', 'c', 'd', 'e', 'f']
list_2 = ['b', 'c', 'f', 'z']

table_format = '{:<10} {:<10}'
print(table_format.format('list_1', 'list_2'))
print('-' * 20)
for x in list_1:
    for y in list_2:
        if x in y:
            print(table_format.format(x, y))
            break
    else:
        print(table_format.format(x,'Missing'))

电流输出：

list_1     list_2    
--------------------
a          Missing   
b          b         
c          c         
d          Missing   
e          Missing   
f          f        

期望的输出：

list_1     list_2    
--------------------
a          Missing   
b          b         
c          c         
d          Missing   
e          Missing   
f          f    
Missing    z

Answer 1

一种解决方案可能是使用包含两个原始列表的所有元素的第三个列表。然后我们可以对新列表进行排序，并在对其进行迭代时，我们可以检查原始列表中是否存在第三个列表的元素。实际上，将第三个列表设为一组会更好。根据Patrick Haugh 的建议，我们也应该在迭代之前将原始列表转换为集合。因此，该过程将更加有效。为什么？关注这个帖子。 Which is faster and why? Set or List?

list_1 = set(['a', 'b', 'c', 'd', 'e', 'f'])  # Or list_1 = {'a', 'b', 'c', 'd', 'e', 'f'}
list_2 = set(['b', 'c', 'f', 'z'])  # list_2 = {'b', 'c', 'f', 'z'}

list_3 = set(list_1 | list_2)
table_format = '{:<10} {:<10}'
print(table_format.format('list_1', 'list_2'))
print('-' * 20)
for elem in sorted(list_3):
    if elem in list_1:
        if elem in list_2:
            print(table_format.format(elem, elem))
        else:
            print(table_format.format(elem, 'Missing'))
    else:
        print(table_format.format('Missing', elem))

输出：

list_1     list_2    
--------------------
a          Missing   
b          b         
c          c         
d          Missing   
e          Missing   
f          f         
Missing    z

Answer 2

使用OrderedDict 似乎可以完成这项工作：

from collections import OrderedDict

list_1 = ['a', 'b', 'c', 'd', 'e', 'f']
list_2 = ['b', 'c', 'f', 'z']

mapping = OrderedDict()
for x in list_1:
    mapping[x] = x if x in list_2 else 'Missing'

for x in list_2:
    mapping[x] = x if x in list_1 else 'Missing'

table_format = '{:<10} {:<10}'
print(table_format.format('list_1', 'list_2'))
print('-' * 20)

for k in mapping:
    if k in list_1:
        print(table_format.format(k, mapping[k]))
    else:
        print(table_format.format(mapping[k], k))

输出：

list_1     list_2    
--------------------
a          Missing   
b          b         
c          c         
d          Missing   
e          Missing   
f          f         
Missing    z      

Answer 3

您也可以使用列表推导来做同样的事情！

>>> print "\n".join(map(str,['list_1\tlist_2\n---------------']+[(each if each in list_1 else 'missing')+'\t'+(each if each in list_2 else 'missing') for each in sorted(set(list_1+list_2))]))
list_1  list_2
---------------
a       missing
b       b
c       c
d       missing
e       missing
f       f
missing z

为了更好地理解，我已经分解了理解！

>>> [each if each in list_1 else 'missing' for each in sorted(set(list_1+list_2))]
['a', 'b', 'c', 'd', 'e', 'f', 'missing']

>>> [each if each in list_2 else 'missing' for each in sorted(set(list_1+list_2))]
['missing', 'b', 'c', 'missing', 'missing', 'f', 'z']

>>> [(each if each in list_1 else 'missing',each if each in list_2 else 'missing') for each in sorted(set(list_1+list_2))]
[('a', 'missing'), ('b', 'b'), ('c', 'c'), ('d', 'missing'), ('e', 'missing'), ('f', 'f'), ('missing', 'z')]

>>> [['list_1','list_2']]+[(each if each in list_1 else 'missing',each if each in list_2 else 'missing') for each in sorted(set(list_1+list_2))]
[['list_1', 'list_2'], ('a', 'missing'), ('b', 'b'), ('c', 'c'), ('d', 'missing'), ('e', 'missing'), ('f', 'f'), ('missing', 'z')]

>>> print "\n".join(map(str,[['list_1','list_2']]+[(each if each in list_1 else 'missing',each if each in list_2 else 'missing') for each in sorted(set(list_1+list_2))]))
['list_1', 'list_2']
('a', 'missing')
('b', 'b')
('c', 'c')
('d', 'missing')
('e', 'missing')
('f', 'f')
('missing', 'z')

>>> print "\n".join(map(str,['list_1\tlist_2\n---------------']+[(each if each in list_1 else 'missing')+'\t'+(each if each in list_2 else 'missing') for each in sorted(set(list_1+list_2))]))
list_1  list_2
---------------
a       missing
b       b
c       c
d       missing
e       missing
f       f
missing z