On 2006-11-08, Farraige <[EMAIL PROTECTED]> wrote:
>
> ...
>
> The main part of my algorithm now looks something like ...
>
> merge(t1, t2, keyColumns, columnsToBeUpdated)
>
> .......
>
> 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 :(
>
> I will be grateful for any ideas
One idea would be to precompute the list comprehensions in the if test.
p2 = [[row_t2[i] for i in keyColums] for row_t2 in t2]
for row_t1 in t1:
proj1 = [row_t1[i] for i in keyColumns]
for row_t1, proj2 in izip(t2, p2):
if proj1 == proj2:
...
--
Antoon Pardon
--
http://mail.python.org/mailman/listinfo/python-list
