R help - Mar 2014 - dummy coding problem

Hi, I have got a problem with dummy coding and I really couldn't figure it
out. Would you please help me out? this is my codes:

idx<-sort(unique(Employment.time$V1));
dummy <- matrix(NA, nrow=nrow(Employment.time), ncol= length(idx))

for (i in 1:nrow(Employment.time)) {

for (j in 1:length(idx)) {

if (Employment.time$V1[i,j] == "Over 4 years") {
dummy[i,j] <- 0
}
else {
dummy[i,j] <- 1
}
}
}

but the R shows that

Error in `[.default`(Employment.time$V1, i, j) :
incorrect number of dimensions

Do you know where is wrong? many thanks!

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