R subtract value for the same ID (from the first ID that shows)

Question

I have a similar question to the question found here: R, subtract value from previous row, group by (slight modification; see below):

In R, lets say I have this da

Answer 1

Using base R, you could do something like this.

res <- lapply(split(Data, Data$id), function(x) {
            x$diff <- x$value - x$value[1]
            x})
res <- do.call(rbind, res)
row.names(res) <- NULL
res
      id     date value diff
1   2380 10/30/12 21.01 0.00
2   2380 10/31/12 22.04 1.03
3   2380  11/1/12 22.65 1.64
4   2380  11/2/12 23.11 2.10
5  20100 10/30/12 35.21 0.00
6  20100 10/31/12 37.07 1.86
7  20100  11/1/12 38.17 2.96
8  20100  11/2/12 38.97 3.76
9  20103 10/30/12 57.98 0.00
10 20103 10/31/12 60.83 2.85