Compute Axis Tickmark Locations (For POSIXct Axis)

Compute pretty tickmark locations, the same way as R does internally. By default, gives the at values which axis.POSIXct(side, x) would use.

Usage

axTicks.POSIXct(side, x, at, format, labels = TRUE, ...)

axTicks.Date(side = 1, x, ...)

Arguments

side

see graphics::axis

x, at

date-time or date object.

format

see base::strptime

labels

either a logical value specifying whether annotations are to be made at the tickmarks, or a vector of character strings to be placed at the tickpoints

...

further arguments to be passed from or to other methods

Value

numeric vector of coordinate values at which axis tickmarks can be drawn.

Details

axTicks has no implementation for POSIXct axis. This function fills the gap.

See also

axTicks(), axis.POSIXct()

Other graphics.layout: abcCoords(), axisBreak(), isValidPlotRegion(), lineToUser(), mar(), plotFacet(), spreadOut()

Examples

with(beaver1, {
  time <- strptime(paste(1990, day, time %/% 100, time %% 100),
                   "%Y %j %H %M")
  plot(time, temp, type = "l") # axis at 4-hour intervals.
  # now label every hour on the time axis
  plot(time, temp, type = "l", xaxt = "n")
  r <- as.POSIXct(round(range(time), "hours"))
  axis.POSIXct(1, at = seq(r[1], r[2], by = "hour"), format = "%H")
  # place the grid
  abline(v=axTicks.POSIXct(1, at = seq(r[1], r[2], by = "hour"), format = "%H"),
         col="grey", lty="dotted")
})