SAMPLE INPUT INPUTFILE.csv
3211111,100,3.2 
3211112,101,3.2 
3211111,100,1.2 
3211112,100,2.2 
3211113,100,5.2 
3211112,100,0.3

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outputfile.csv 
3211111,100,4.4 
3211112,100,2.5
3211112,101,3.2
3211113,100,5.2