I had a dataset as a result of groupby as :
CUSTID TRANSACTION_ID COUNT
CU_1 TR_1 1
CU_1 TR_2 1
CU_1 TR_3 1
CU_2 TR_4 1
CU_2 TR_5 1
I needed to have result as CUSTID TOTAL_COUNT
CU_1 3
CU_2 2