在R中，如何根据另一列的子集定义df中的新列？

Question

I have time series data in a data frame. Let's say I have one column of dates, one column of values, and I want to create a new column that is the sum of all values before the date index. Is there a better solution than using a for loop?

For example:

table = data.frame(date=seq(1,5),values=c(3,2,4,1,5))
table$sum = ...??

Answer 1

For this you can use cumsum :

table = transform(table, sum_value = cumsum(values))
table
  date values sum_value
1    1      3         3
2    2      2         5
3    3      4         9
4    4      1        10
5    5      5        15