I have a dynamic created crosstab with data of customer's billing. I
want to define a DataWindow.Crosstab.Rows expression for group the
customers with "low" billing.
In this example I tried with if( grand_total_billing < 70,
customer,'Others') but this does not work:

I have:
CUSTOMER Q1 Q2 Q3 TOTAL
Customer 1 10 10
Customer 2 8 3 11
Customer 3 20 20 30 70
Customer 4 10 5 5 20
Customer 5 5 40 70 115
Customer 6 20 60 30 110
Customer 7 5 5 15 25
TOTAL 68 140 153 361

and I want:
CUSTOMER Q1 Q2 Q3 TOTAL
Customer 3 20 20 30 70
Customer 5 5 40 70 115
Customer 6 20 60 30 110
Others (4) 23 20 23 66
TOTAL 68 140 153 361

Thanks in advance,
jorge.