Loop for ARMA model estimation

Question

Suppose that I have the following "for" loop in R.

USDlogreturns=diff(log(prices))

for(i in 0:5){
  for(j in 0:5){
    fit <- arima(USDlogreturns, order=c(i,0,j), include.mean=TRUE)
     }
}

How do you tell R to substitute a NA matrix with the coefficients of all the estimated models?

Answer 1

You will need a matrix M with dimensions 36 times 13. Then use

M=matrix(NA,36,13)
k=0 # current row being filled in
for(i in 0:5){
  for(j in 0:5){
    k=k+1
    fit <- arima(USDlogreturns, order=c(i,0,j), include.mean=TRUE)
    if(i>0) M[k,c(1:   i) ]=fit$coef[c(   1 :   i )] # AR coefficients in the 2nd-6th columns
    if(j>0) M[k,c(8:(7+j))]=fit$coef[c((i+1):(i+j))] # MA coefficients in the 8th-12th columns
            M[k,      13  ]=tail(fit$coef,1)         # "intercept" (actually, mean) in the 13th column
  }
}

The columns 2 to 6 will contain AR coefficients.
The columns 8 to 12 will contain MA coefficients.
The 13th column will contain the "intercepts" (actually, the means, as the terminology in the arima function is misleading).