Convert from annual to quarterly data, constrained to annual average

Question

I have several variables at annual frequency in R that I would like to include in a regression analysis with other variables available at quarterly frequency. Additionally,

Answer 1

Perhaps I'm missing something here, but assuming the annual value always comes from the first quarter, couldn't you just replace mean in your aggregate call with min?

 > d <- aggregate(c, as.integer(format(index(c),"%Y")), min, na.rm=TRUE)
 > d
      z_a z_q
 2000 100 100
 2001 110 110
 2002 111 111