Hello guys, I'm having some trouble on figuring out how to create a new column with the sum of 2 subsequents cell.

supose I have df1<- tibble(Years=c(1990, 2000, 2010, 2020, 2030, 2050, 2060, 2070, 2080),

Values=c(1,2,3,4,5,6,7,8,9 ))

Now, I want a new column where the first line is the sum of 1+2, the second line is the sum of 1+2+3 , the third line is the sum 1+2+3+4 and so on.

As 1, 2, 3, 4... are hipoteticall values, I need to measure the absolute growth from a decade to another in order to create later on a new variable to measure the percentage change from a decade to another.

I hope I made sense.

Thanks in advance for any help.