Adding points to plot.ts, when start, end and frequency are set

Question

I have problem with adding points to plot.ts. If I create ts object as in example below, everything is fine and points are added to the plot.

data <- ts(rnorm(100))
plot(data)
ind <- c(1,10,67)
points(ind, data[ind], pch = 19, col = 'red')

But when I do this in that way (I would like to have dates on the X axis, so I use start, end and frequency arguments.), points don't appear on the plot:

data <- ts(rnorm(100), start = c(1996,1), end = c(2004,4), frequency = 12)
plot(data)
ind <- c(1,10,67)
points(ind, data[ind], pch = 19, col = 'red')

Is there any option to add those points or add dates to the first example?

PS. I am almost sure, that I have once managed to add one point to plot by referring to the value of time series in specific date, but now I can't bring it back.

Answer 1

This works for me:

data <- ts(rnorm(100), start = c(1996,1), end = c(2004,4), frequency = 12)
plot(data)
ind <- 1996 + c(0,9,66)/12
points(ind, data[c(1,10,67)], pch = 19, col = 'red')

Answer 2

I would rather use the zoo package:

data <- as.zoo(data)
plot(data)
ind <- c(1,10,67)
points(data[ind], pch = 19, col = 'red')

That way you can play with the index without having to worry about the date (it seemed to me that is what you wanted).