Highlight (shade) plot background in specific time range

Using alpha transparency:

x <- seq(as.POSIXct("1949-01-01", tz="GMT"), length=36, by="months")y <- rnorm(length(x))plot(x, y, type="l", xaxt="n")rect(xleft=as.POSIXct("1950-01-01", tz="GMT"),     xright=as.POSIXct("1950-12-01", tz="GMT"),     ybottom=-4, ytop=4, col="#123456A0") # use alpha value in colidx <- seq(1, length(x), by=6)axis(side=1, at=x[idx], labels=format(x[idx], "%Y-%m"))

or plot highlighted region behind lines:

plot(x, y, type="n", xaxt="n")rect(xleft=as.POSIXct("1950-01-01", tz="GMT"),     xright=as.POSIXct("1950-12-01", tz="GMT"),     ybottom=-4, ytop=4, col="lightblue")lines(x, y)idx <- seq(1, length(x), by=6)axis(side=1, at=x[idx], labels=format(x[idx], "%Y-%m"))box()

Here is a solution that uses zoo simply because that makes the subsetting easy. You could do the same with standard indexing as well:

## create a long monthly sequence and a sub-sequencemonths <- seq( as.Date("1950-01-01"), as.Date("2009-12-12"), by="month")subset <- seq( as.Date("1970-01-01"), as.Date("1979-12-31"), by="month")## generate some random valuesset.seed(42)values <- cumsum(rnorm(length(months)))## plot as a zoo object, overlay a gray background and overplot a line in redlibrary(zoo)Z <- zoo(values, months)plot(Z)rect(xleft=head(subset,1), xright=tail(subset,1),     ybottom=par("usr")[3], ytop=par("usr")[4],     density=NA, col="lightgray")lines(Z[subset], col='red')box()

_{(source: eddelbuettel.com)}

By using par("usr") we avoid the need for explicit values for upper and lower region marks. And the zoo indexing makes finding the start- and endpoints easy. This would work the same way for data in different time resolutions.

You can use the chartSeries() function in quantmod with an xts timeSeries and the addTA() function to add the background highlighting:

addTA(xts(rep(TRUE,length(times)), times), on=-1, col="#333333", border=NA)