[R] lag, count

[Val]

Hi all,

I want sort the data by ID and Y2 then count the number of rows within
IDs.  Assign a "flag" variable to reach row starting from first  to
the last row.
For instance, in the following data ID "1" has three rows   and each
row is assigned flag sequentially 1, 2,3.

2. In the second step, within each ID, I want get the difference
between the subsequent row values of y1 and y2(date) values.
Within each ID the first value of y1diff  and y2diff are always 0. The
second values for each will  be the current row minus the previous
row.



lag<-read.table(text=" ID, y1, y2
ID,Y1,y2
1,0,12/25/2014
1,125,9/15/2015
1,350,1/30/2016
2,0,12/25/2012
2,450,9/15/2014
2,750,1/30/2016
2,  656, 11/30/2016
",sep=",",header=TRUE)

output looks like as follows

ID,flag,y1,y2,y1dif,y2dif
1,1,0,12/25/2014,0,0
1,2,125,9/15/2015,125,264
1,3,350,1/30/2016,225,137
2,1,0,12/25/2012,0,0
2,2,450,9/15/2014,450,629
2,3,750,1/30/2016,300,502
2, 4, 656 11/30/2016, -94, 305

Thank you