Hi I need your help...
I am implementing the method that updates given table (table is
represented as list of lists of strings) according to other table (some
kind of merging)...
This method takes following arguments:
t1 - table we would like to update
t2 - table we would like to take data
from
keyColumns - list of key indexes e.g. [0,1]
columnsToBeUpdated - list of column indexes we would like to update in
our table T1 e.g [2,4]
Let's say we have a table T1:
A B C D E
---------------
1 4 5 7 7
3 4 0 0 0
and we call a method mergeTable(T1, T2, [0,1], [2,4])
It means that we would like to update columns C and E of table T1 with
data from table T2 but only in case the key columns A and B are equal
in both tables.... I grant that the given key is unique in both tables
so if I find a row with the same key in table T2 I do merging, stop and
go to next row in table T1...
Let's say T2 looks following:
A B C D E
---------------
2 2 8 8 8
1 4 9 9 9
So after execution of our mergeTable method, the table T1 should look
like :
A B C D E
1 4 9 7 9
3 4 0 0 0
The 2nd row ['3', '4', '0' ,'0', '0'] didn't change because there was
no row in table T2 with key = 3 ,4
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
Thanks in advance!
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