lattice alternating axis tick marks

axis-ticks.R

# alternating axis tick marks
# Bryan Urban
# 2015-06-01

xscale.components.alt <- function(lim, by=5, ...){
  ans <- xscale.components.default(lim, ...)
  
  tck.at  <- ans$bottom$ticks$at 
  tck.lab <- as.character(tck.at)
    
  ind <- length(tck.at)
  tck.major <- tck.at[seq(1, ind, by=by)]
  major <- tck.at %in% tck.major
  tck <- ifelse(major, 2, 1)
  tck.lab[!major] <- ""
  
  ans$bottom$labels$labels <- tck.lab
  ans$bottom$ticks$tck <- tck
  ans$bottom$labels$check.overlap = FALSE
  ans  
}

xyplot(mpg ~ hp, mtcars,
       xlim=c(20, 560),
       scales=list(x=list(at=seq(25,550, by=5))),
       xscale.components = xscale.components.alt
       )