[R] Formula that includes previous row values

[Pele]

Hi Jorge - many thanks for you suggestion, but I am looking for a way where I
don't have to use a loop.  I meant to include that in my description.

Thanks again!


Jorge Ivan Velez wrote:
> 
> 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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>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 

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