I have around 30-35 csv files . some sample is like First File

NAME CLIENT VAL1 VAL2 VAL3
aa   bb       4   4    5
aa   cc       4   4    5
Second File
aa   bb       4   4    5.34
aa   dd       4   4    4.05
THird File
aa   bb       4   4    5.34
aa   dd       4.1  4.3    4.05
aa   ff       4.3   0    3.4
[download]

My task is to merge them to a single file in format like

NAME CLIENT VAL1 VAL2 VAL3
aa  bb      <sum from allfiles> <sum from all files> <do>
aa cc        -------- do -----------
aa dd        -------  do ----------
[download]

In practice each file is very big containing around 8-9 k lines. I have written some code which gives the result but it is taking time around 25-30 minutes. I am looking for a solution which can take less time may b by using parallel processing or watever

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