# [R] for (i in...)

William Revelle lists at revelle.net
Mon Dec 10 01:21:51 CET 2007

```At 3:27 PM -0500 12/9/07, Duncan Murdoch wrote:
>On 09/12/2007 3:04 PM, Rina Oldager Miehs wrote:
>>  Hey
>>
>>  do anyone know why this error occurs??
>>
>  >> for(i in 1:n_trait){
>>  +    for( j in 1:n_trait){
>>  +    rG[i,j] <- (G_o[i,j]/(sqrt(G_o[i,i]%*%G_o[j,j]))
>>  +    rP[i,j] <- (P_o[i,j]/(sqrt(P_o[i,i]%*%P_o[j,j]))
>>  Error: unexpected symbol in:
>  > "   rG[i,j] <- (G_o[i,j]/(sqrt(G_o[i,i]%*%G_o[j,j]))
>>     rP"
>
>Your parentheses don't match on the rG line.  You have 3 lefts and 2 rights.
>
>Duncan Murdoch

Rina,
Alternatively, you could avoid the entire double loop by using
matrix operations.  I show this and then reproduce it using the first

#how to use matrices to avoid looping
n_trait <- 5
X <- matrix( rnorm(100*n_trait),ncol= n_trait) #create a data matrix
G_o <- t(X) %*% X   #create the G_o matrix as a  matrix of cross products
G_o          #show the cross products

dG <- diag(1/sqrt(diag(G_o)))  #divide by the sqrt of the diagonal
rG <- dG %*% G_o %*% dG
rG                              #show the result
#######################
#abbreviated Rina code using loops
for(i in 1:n_trait){
for( j in 1:n_trait){
rG[i,j] <- G_o[i,j]/(sqrt(G_o[i,i]%*%G_o[j,j])) }}
rG         #compare to above

Bill

--
William Revelle		http://personality-project.org/revelle.html
Professor			http://personality-project.org/personality.html
Department of Psychology             http://www.wcas.northwestern.edu/psych/
Northwestern University	http://www.northwestern.edu/
Use R for statistics:                          http://personality-project.org/r

```