# [R] Formula that includes previous row values

Pele drdionc at yahoo.com
Mon Feb 23 21:59:18 CET 2009

```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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```