please help with optimisation of this code - update of given table according to another table

Gabriel Genellina gagsl-py at
Wed Nov 8 20:23:23 CET 2006

At Wednesday 8/11/2006 07:18, Farraige wrote:

>         for row_t1 in t1:
>             for  row_t2 in t2:
>                 if [row_t1[i] for i in keyColumns] == [row_t2[j] for j
>in keyColumns]:
>                     # the keys are the same
>                     for colName in columnsToBeUpdated:
>                         row_t1[colName] = row_t2[colName]
>                     # go outside the inner loop - we found a row with
>                     # the same key in the table
>                     break
>In my algorithm I have 2 for loops and I have no idea how to optimise
>it (maybe with map? )
>I call this method for very large data and the performance is a
>critical issue for me :(

def getkey(row):
   return tuple([row[i] for i in keyColumns])

Sort both tables using .sort(key=getkey); then traverse both in 
paralell like in classic merge; in 1 pass you get the job done (not 
counting the two initial sorts)

Gabriel Genellina
Softlab SRL 

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