我有data：
Purshased_Date value Refund_Date MONTH YEAR MDY INTNX
2015-08-14 0 2015-08-14 8 2015 2015-08-01 2015-08-31
2015-08-14 96 NA 8 2015 2015-08-01 2015-08-31
2015-08-14 127 NA 8 2015 2015-08-01 2015-08-31
我想通过计算上面的数据来创建一个新列 代码是：
library(data.table)
data[, NewCol := value * pmax(0, difftime(pmin(Refund_Date, INTNX), pmax(Purshased_Date, MDY-1), units = 'day')) / as.numeric(difftime(INTNX, MDY-1, units = 'day'))]
但是，在pmin(Refund_Date1, INTNX) = NA时，R会考虑Refund_Date = NA
我不想使用NA
我想要的是Refund_Date = NA，pmin(Refund_Date, INTNX) = INTNX
我想要的结果如下：
Purshased_Date value Refund_Date MONTH YEAR MDY INTNX NewCol
2015-08-14 0 2015-08-14 8 2015 2015-08-01 2015-08-31 0
2015-08-14 96 NA 8 2015 2015-08-01 2015-08-31 52.64516129
2015-08-14 127 NA 8 2015 2015-08-01 2015-08-31 69.64516129
我该怎么办？有什么建议吗？