通过变量列表执行滚动求和的优雅，快速方法

Has anyone developed an elegant, fast way to perform a rolling sum by date? For example, if I wanted to create a rolling 180-day total for the following dataset by Cust_ID, is there a way to do it faster (like something in data.table). I have been using the following example to currently calculate the rolling sum, but I am afraid it is far to inefficient.Has anyone developed an elegant, fast way to pe