Question

I’m trying to plot some prices vs dates. There are about 10k lines of data. The dates are a range from ~ 7/1/2008 – 12/1/2011. I’d like to be able to create a custom x-axis with the following ticks on it for each year:

1) at 1/1 have the YYYY (ie 2011)

2) at 4/1 have the abbreviation of the month (ie Apr)

3) at 7/1 have the abbreviation of the month (ie Jul)

4) at 10/1 have the abbreviation of the month (ie Oct)

Here’s a description of the data:

> head(as.POSIXct(rs4p[,3]))
[1] "2008-06-30 20:00:00 EDT" "2008-06-30 20:00:00 EDT"
[3] "2008-06-30 20:00:00 EDT" "2008-06-30 20:00:00 EDT"
[5] "2008-06-30 20:00:00 EDT" "2008-06-30 20:00:00 EDT"
> head((rs4p[,3]))
[1] "2008-07-01" "2008-07-01" "2008-07-01" "2008-07-01" "2008-07-01"
[6] "2008-07-01"
> min((rs4p[,3]))
[1] "2008-07-01"
> max((rs4p[,3]))
[1] "2011-12-08"
> class((rs4p[,3]))
[1] "Date"

UPDATE:

One other thing I forgot is that when the graph is done I’d like to put a grid() over the plot. Is there a way to make the grid lines correspond to the year ticks?

Answer 1

Vincent got it first, but here’s my version with zoo

library(zoo)
my.ts <-zoo(0:1000,as.Date("2000-01-01")+0:1000)
plot(my.ts, xaxt="n")

years <-index(my.ts)[format(index(my.ts),"%m-%d") %in% "01-01"]
other.quarters <- index(my.ts)[ format(index(my.ts), "%m-%d") %in% c("04-01", "07-01","10-01")]
axis.Date(1, at=years, label=format(years,"%y"))
axis.Date(1, at=other.quarters, label=format(other.quarters, "%b"))

UPDATE: Here’s how to add gridlines:

grid(nx=NA, ny=NULL)
abline(v=c(years, other.quarters),col = "lightgray", lty = "dotted", lwd = par("lwd"))