Summing/combining tuples

[Larry Hudson]

On 05/18/2016 09:53 PM, DFS wrote:
> On 5/18/2016 10:58 PM, Larry Hudson wrote:
[snip...]
>> Why two loops?  Put both summations in a single loop.  Then you're only
>> scanning the alist once instead of twice.
>>
>> groups1 = defaultdict(int)
>> groups2 = defaultdict(int)
>> for nm, matches, words in alist:
>>     groups1[nm] += matches
>>     groups2[nm] += words
>>
>>      -=- Larry -=-
>
>
> That gives me two lists - how do I combine them?
>
> In the end that'll be at least 6 lines of code.  Do you have a one-liner to summarize the data?
>
> Thanks
>
One-liner?  No way.  I did manage to get the whole conversion down to 6 lines...
(And I am far from an expert pythonista, a more experienced/expert programmer can probably do 
better.)

A two-line helper function
A two-line for loop
A one-line list comprehension
One line to declare a dictionary as an intermediate variable

#  A helper function -- adds two tuples
#  Could add square brackets to return a 2-element list instead of
#  a tuple, but the final result is the same either way.
def addtpl(t1, t2):
     return t1[0]+t2[0], t1[1]+t2[1]

#  Accumulate alist data into an intermediate temporary dictionary
tdic = {}
for dat in alist:
     tdic[dat[1]] = addtpl(tdic.get(dat[1], (0,0)), dat[2:])

#  Convert the dictionary back to a list of tuples
result = [(str(n), tdic[n][0], tdic[n][1]) for n in tdic]

Of course, this doesn't retain the original order, but you can use the sorted() function to sort 
the results by the names.

Here is the same thing as a single function that returns the sorted list...
(It also automatically throws away the temporary dictionary.  But it's now 7 lines because of 
the added def line.)

def combine(lst):
     def addtpl(t1, t2):
         return [t1[0]+t2[0], t1[1]+t2[1]
     tdic = {}
     for dat in lst:
         tdic[dat[1]] = addtpl(tdic.get(dat[1], (0,0)), dat[2:])
     return sorted([(str(n), tdic[n][0], tdic[n][1]) for n in tdic])

      -=-Larry -=-