[R] Incremental

[Val]

Hi all,

I have a data set like
dat<-read.table(text=" y1, flag
39958,S
40058,R
40105,X
40294,H
40332,S
40471,R
40493,R
40533,X
40718,H
40771,S
40829,R
40892,X
41056,H
41110,S
41160,R
41222,R
41250,R
41289,R
41324,X
41355,R
41415,X
41562,X
41562,H
41586,S
",sep=",",header=TRUE)

First sort the data by y1.
Then
I want to create two columns .
1. the first new column is  (x1):  if flag is "S"  then  x1=1  and
assign the following/subsequent rows 1 as well.   When we reach to
the next "S"  then  x1=2 and the subsequent rows will be assigned to
2.

2. the second variable (z2). Within each x1 find the difference
between the first y1 and subsequent y1 values

Example  for the first few rows
  y1,   flag, x1, z2
39958, S, 1,    0          z2 is calculated as     z2=(39958, 39958)
40058, R, 1, 100         z2 is calculated as     z2=(40058, 39958)
40105, X, 1, 147         z2 is calculated as     z2=(40105, 39958)
40294, H, 1, 336         z2 is calculated as     z2=(40294, 39958)
40332, S, 2,  0            z2 is calculated as     z2=(40332, 40332)
etc

Here is the complete output for the sample  data
39958,S,1,0
40058,R,1,100
40105,X,1,147
40294,H,1,336
40332,S,2,0
40471,R,2,139
40493,R,2,161
40533,X,2,201
40718,H,2,386
40771,S,3,0
40829,R,3,58
40892,X,3,121
41056,H,3,285
41110,S,4,0
41160,R,4,50
41222,R,4,112
41250,R,4,140
41289,R,4,179
41324,X,4,214
41355,R,4,245
41415,X,4,305
41562,X,4,452
41562,H,4,452
41586,S,5,0

Val