use split and lapply to make it easier. Substitute in your own
calculations since this is just an example:
> x
id t X1 X2
1 1 1 4 3
2 1 2 9 2
3 1 3 7 3
4 1 4 6 6
5 2 1 6 4
6 2 2 5 3
7 2 3 1 1
8 3 1 9 6
9 3 2 5 5
> # first split the data by 'id'
> x.s <- split(x, x$id)
> # then process each group
> result <- lapply(x.s, function(.grp){
+ output <- .grp[1, 3:4] * 4 # data from the first row
+ i <- 2
+ # repeat for the rest of the row
+ while (i <= nrow(.grp)){
+ output <- output + .grp[i, 3:4] * 2
+ i <- i + 1
+ }
+ output # return value
+ })
> result
$`1`
X1 X2
1 60 34
$`2`
X1 X2
5 36 24
$`3`
X1 X2
8 46 34
>
On Tue, Dec 7, 2010 at 5:43 PM, Anup Nandialath
<anup_nandial...@yahoo.com> wrote:
> Dear R-helpers,
>
> I have a basic question on using loops.
>
> I have a panel data set with different variables measured for "n" firms over
> "t" time periods. A snapshot of the data is given below
>
> id t X1 X2
> 1 1 4 3
> 1 2 9 2
> 1 3 7 3
> 1 4 6 6
> 2 1 6 4
> 2 2 5 3
> 2 3 1 1
> 3 1 9 6
> 3 2 5 5
>
> thus total sample n=9
>
> My problem is as follows. I need to do some computations on the data where
> the first observation for each firm (ie. id=1 and t=1; id=2 and t=1; id=3 and
> t=1) requires a specific operation on x1 and x2 and the subsequent operations
> are based on the computed value of the first operation.
>
> For example the pseudocode is as follows
>
> ##define output matrix
>
> output <- rep(0,n)
>
> ## define coefficient vector
> b <- c(1,1)
>
> for (i in 1:number of simulations)
> {
> for (j in 1:id)
> {
> for(k in 1:t)
> {
> if(Data$t[,2]==1)
> {
> meanvec <- Data[k,3:4]%*%b
> output[k] = calc (meanvec) # output from calc is a scalar
> }
> else
> output[k]= calc(a*output[k-1]+Data[k,3:4]%*%b)
> }
> }
> }
>
> Thus the end result should be a vector "output" with nine observations based
> on the computations.
>
> I hope the problem is clear and I greatly appreciate any help in solving this
> problem . Thanks in advance for your help.
>
> Kind Regards
>
> Anup
>
>
>
>
> [[alternative HTML version deleted]]
>
>
> ______________________________________________
> R-help@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.
>
>
--
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?
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