Message-ID: <AANLkTinwVaNqzJ7yErpgKUX2jUqd5e4_HcJE-tjD1hN_@mail.gmail.com>
Date: 2010-12-08T01:47:19Z
From: jim holtman
Subject: Help on loops
In-Reply-To: <657227.72598.qm@web53303.mail.re2.yahoo.com>
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
$`3`
X1 X2
8 46 34
>
On Tue, Dec 7, 2010 at 5:43 PM, Anup Nandialath
<anup_nandialath at yahoo.com> wrote:
> Dear R-helpers,
>
> I have a basic question on using loops.
>
> I have a panel data set with different variables measured for "n" firms over "t" time periods. A snapshot of the data is given below
>
> id??? t??? X1??? X2
> 1??? 1?? ? 4??? 3
> 1??? 2??? 9??? 2
> 1??? 3??? 7??? 3
> 1??? 4??? 6??? 6
> 2??? 1??? 6??? 4
> 2??? 2??? 5??? 3
> 2??? 3??? 1??? 1
> 3??? 1??? 9??? 6
> 3??? 2??? 5??? 5
>
> thus total sample n=9
>
> My problem is as follows. I need to do some computations on the data where the first observation for each firm (ie. id=1 and t=1; id=2 and t=1; id=3 and t=1) requires a specific operation on x1 and x2 and the subsequent operations are based on the computed value of the first operation.
>
> For example the pseudocode is as follows
>
> ##define output matrix
>
> output <- rep(0,n)
>
> ## define coefficient vector
> b <- c(1,1)
>
> for (i in 1:number of simulations)
> {
> ?? for (j in 1:id)
> ??? {
> ????? for(k in 1:t)
> ???????? {
> ?????????? if(Data$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 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.
>
>
--
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?