[R] For Loops

[kjetil halvorsen]

Hola!

fr <- data.frame(id=c(1,1,2,2,3,3,4,4), x=rnorm(8), y=rnorm(8))

> for (i in 1:4) { temp <- fr[fr$id==i,]
+                   print(temp)}
  id         x         y
1  1 -1.817315 -0.940551
2  1  1.511910  1.306569
  id          x         y
3  2 -1.3677349 0.5242760
4  2  0.4932293 0.4221455
  id         x          y
5  3 0.0975871 -1.6131919
6  3 0.1439102 -0.4736377
  id         x          y
7  4 0.4927572  1.2780839
8  4 0.3018717 -0.8101557
> 

for the second Q I think you want something like
Y[i,]

not Y[[i]] --- that is for lists.

Kjetil Halvorsen

Isabel Jones wrote:
> 
> Hi all
> 
> Perhaps someone could help me?
> 
> I am running a loop from i=1 to n
> 
> In my data.frame I have a list of i.d's (i=1 to n) and
> each i.d has 2
> rows of data (representing 2 time points) e.g.
> 
> id  Y   X1   X2
>  1   1   0     0
>  1   0   0     0
>  2   1   1     0
>  2   1   1     0
> 
> I am wanting to put into my 'for' loop, a line which
> can pick out the
> rows where id=i and call this a temporary name while
> it executes some
> commands beforing moving on to the next i. I'm not
> sure what command I
> can use to locate these rows where id=i and store them
> in a temporary
> matrix.
> 
> Also when I have say a matrix consisting of all values
> of Y - how can I
> refer to the Y for person i i.e. Yi
> I have seen in the R information that I can use
> Y[[i]]?
> Is it possible to write say Y[[i]]<-x[[i]]*5
> 
> Can somebody point me in the right direction as to how
> to use indexing?
> 
> Cheers to all
>    Isabel
> 
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