How to use msum to sum only positive numbers in DolphinDB

Question

I have a column numbers, positive or negative, such as the Val column in the table below;

msg = table(1..100 as id, rand(-100..100,100) as Val)

Now I want to calculate the moving summation for Val with the rolling window of length 10 ,but only calculate positive numbers in Val.Something like select msum( if(val>0), 10) from msg.

Answer 1

使用函数iif将所有负数转换为零，然后使用msum计算滚动和。

msum(iif(val > 0, val, 0), 10)