Linear model singular because of large integer datetime in R?

Question

Simple regression of random normal on date fails, but identical data with small integers instead of dates works as expected.

# Example dataset with 100 observati         


        

Answer 1

Yes, it could. QR factorization is stable, but is not almighty God.

X <- cbind(1, 1e+11 + 1:10000)
qr(X)$rank
# 1

Here the X is like the model matrix for your linear regression model, where there is a all-1 column for intercept, and there is a sequence for datetime (note the large offset).

If you center the datetime column, these two columns will be orthogonal hence very stable (even when solving normal equation directly!).