"Paul McGuire" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> "J. Clifford Dyer" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
>> ZeD wrote:
>>> Paul Rubin wrote:
>>>
>>>>> A = [0,1,2,3,4,5,6,7,8,9,10]
>>>>> B = [2,3,7,8]
>>>>>
>>>>> desired_result = [2,3,7,8,0,1,4,5,6,9,10]
>>>> How about:
>>>>
>>>> desired_result = B + sorted(x for x in A if x not in B)
>>>
>>> this. is. cool.
>>>
>>
>> Cool, yes, but I'm not entirely sure it does what the OP wanted. Partly
>> because I'm not entirely sure what the OP wanted. Counter example:
>>
>> Given these variables:
>>
>> A = [0,1,2,3,4,5,6,8,9,10] # Note 7 is missing
>> B = [2,3,7,8]
>>
>> which of the following should the function yield?
>>
>
> From the original post:
>
> "I have two lists, A and B, such that B is a subset of A."
>
> So this is not a case that needs to be supported.
>
> I envisioned something like the OP had a sequence of items to start with,
> did a random sampling from the list, and wanted to move the sampled items
> to the front of the list.
>
> -- Paul
>
Here is a little subclass of list that has some set-ish operators added.
-- Paul
# ListWithMath does set-like operations on lists, keeping list order
# stable where applicable
class ListWithMath(list):
def isSuperset(self,other):
return len(self ^ other) == len(other)
def __iadd__(self,other):
self.extend(other)
return self
def __isub__(self,other):
if self.isSuperset(other):
for i in other:
self.remove(i)
return self
else:
raise ValueError
def __ixor__(self,other):
for a in self[::-1]:
if not a in other:
self.remove(a)
return self
def __add__(self,other):
temp = ListWithMath(self)
temp += other
return temp
def __sub__(self,other):
temp = ListWithMath(self)
temp -= other
return temp
def __xor__(self,other):
temp = ListWithMath(self)
temp ^= other
return temp
def __radd__(self,other):
return ListWithMath(other) + self
def __rsub__(self,other):
return ListWithMath(other) - self
def __rxor__(self,other):
return ListWithMath(other) ^ self
A = ListWithMath( [0,1,2,3,4,5,6,7,8,9,10] )
B = ListWithMath( [2,3,7,10,8] )
print "%s+(%s-%s)" % (B,A,B)
C = B+(A-B) # union and exclusion
print C
D = ListWithMath( [1,2,3,6,8,11] )
print "%s ^ %s" % (B,D)
print B^D # intersection
print "%s ^= %s" % (B,D)
B ^= D # in-place intersection
print B
print C
C += []
print C
C -= []
print C
C ^= []
print C
Prints:
[2, 3, 7, 10, 8]+([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]-[2, 3, 7, 10, 8])
[2, 3, 7, 10, 8, 0, 1, 4, 5, 6, 9]
[2, 3, 7, 10, 8] ^ [1, 2, 3, 6, 8, 11]
[2, 3, 8]
[2, 3, 7, 10, 8] ^= [1, 2, 3, 6, 8, 11]
[2, 3, 8]
[2, 3, 7, 10, 8, 0, 1, 4, 5, 6, 9]
[2, 3, 7, 10, 8, 0, 1, 4, 5, 6, 9]
[2, 3, 7, 10, 8, 0, 1, 4, 5, 6, 9]
[]
--
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