Formula that includes previous row values

Dear Pele,
Probably not the best way to proceed but it works:

X<-read.table(textConnection("ID      X2
1.00    1.00
2.00    0.00
3.00    1.00
4.00    3058
5.00    0.00
6.00    6.00"),header=TRUE)
closeAllConnections()
X

x3<-0
for(i in 2:(nrow(X)+1)) x3<-c(x3, X$X2[i-1]+0.24*x3[i-1])
X$x3<-x3[-1]
X

HTH,

Jorge


On Mon, Feb 23, 2009 at 3:59 PM, Pele <drdionc at yahoo.com> wrote:

Hi R users,

Is there an easy way in R to generate the results table below using table
1
and the formula (simplified version of the real problem)?  It would be
easy
if I knew the R equivalent of SAS's retain function, but could not find
one.

Thanks in Advance for any help!

table1:

ID      X2         X3
1.00    1.00       0
2.00    0.00
3.00    1.00
4.00    3058
5.00    0.00
6.00    6.00

Formula: X3 = x2 + (.24 * x3)

where the values in the x3 column of the result table are retained from
previous x3 rows.. Also the first x3 value is initialized to 0 to start

e.g.
       for ID=1 we have  1 + .24(0)                    = 1.00
       for ID=2 we have  0 + .24(1)                    = 0.24
       for ID=3 we have  1 + .24(.24)          = 1.06
       for ID=4 we have  3058 + .24(1.06)      = 3058.25
       etc.............

Results:
ID      X2      x3
1.00    1.00    1.00
2.00    0.00    0.24
3.00    1.00    1.06
4.00    3058    3058.25
5.00    0.00    733.98
6.00    6.00    182.16
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