如何使用不完整的日期列基于R中的动态日期差异有效地创建变更变量

I have a dataset containing the price and market cap of a stock for a date range. Some dates are missing between the date range. I want to efficiently create new variables that show how much the current price changed from the price x days ago (where x is a list of numbers representing day differences). I have a dataset containing the price and marke