DPD_30-180+(-DPD30_flag); is equvivalent to DPD_30_180=DPD_30_180-DPD30_flag; ( plus: DPD_30_180 becomes retained ) I just wanted to make that line very similar to the previous sum statment (and I also copy-pasted it from there): DPD_30_180+180_DPD30_flag; But this one would be syntactically wrong: DPD_30-180-DPD30_flag; - it is not a sum statement. My code interleaves the original dataset and 2 shifted datasets. When I read a record from the original dataset, I need to add to the cummulative variables. When I read from the shifted dataset, I need to substract. It is because after 6 (or 12) months the effect of the DPD_XX variable "expires".
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