David,
To make the percentage splits to capture the cases that compose 20/40/80% of the cumulative transaction value I made the following adjustments
SORT CASES BY Transaction_Value.
CREATE Cum_Value_of_Transactions=CSUM(Transaction_Value).
AGGREGATE OUTFILE=* MODE=ADDVARIABLES
/Total_Value_of_Transactions=SUM(Transaction_Value).
DO IF $CASENUM EQ 1.
+ DO REPEAT PCT= 20 40 80/V=#pct20 #pct40 #pct80.
+ COMPUTE V=PCT/100*Total_Value_of_Transactions.
+ END REPEAT.
END IF.
NUMERIC #Bin.
VECTOR #P=#Pct20 TO #Pct80.
DO IF #Bin LT 4.
+ IF #P(#Bin+1) LT Cum_Value_of_Transactions #Bin=#Bin+1.
END IF.
COMPUTE Bin=#Bin+1.
FREQ Bin.