line connecting missing data R

Question

I would like a line plot in R of the days a bird spent away from its nest. I have missing data that is making it difficult to show the general trend. I want to replace the line for the days that I don't have information for with a dotted line. I have absolutely no idea how to do this. Is it possible to do in R?

     > time.away.1
   hrs.away days.rel
1     0.380       -2
2     0.950       -1
3     1.000        0
4     0.200        1
5     0.490       12
6     0.280       13
7     0.130       14
8     0.750       20
9     0.160       21
10    1.830       22
11    0.128       26
12    0.126       27
13    0.500       28
14    0.250       31
15    0.230       32
16    0.220       33
17    0.530       40
18    3.220       41
19    0.430       42
20    1.960       45
21    1.490       46
22   24.000       56
23   24.000       57
24   24.000       58
25   24.000       59
26   24.000       60
27   24.000       61

My attempt:

plot(hrs.away ~ days.rel, data=time.away.1,
     type="o",
     main="Time Away Relative to Nest Age",
     ylab="Time spent away",
     xlab="Days Relative to Initiation",
     ylim=c(0,4))

Answer 1

Here is a way using diff to make a variable determining if a sequence is missing. Note that I renamed your data to dat

## make the flag variable
dat$type <- c(TRUE, diff(dat$days.rel) == 1)

plot(hrs.away ~ days.rel, data=dat,
     type="p",
     main="Time Away Relative to Nest Age",
     ylab="Time spent away",
     xlab="Days Relative to Initiation",
     ylim=c(0,4))
legend("topright", c("missing", "sampled"), lty=c(2,1))

## Add line segments
len <- nrow(dat)
with(dat,
     segments(x0=days.rel[-len], y0=hrs.away[-len],
              x1=days.rel[-1], y1=hrs.away[-1],
              lty=ifelse(type[-1], 1, 2),
              lwd=ifelse(type[-1], 2, 1))
     )

For the ggplot version, you can make another data.frame with the lagged variables used above,

library(ggplot2)
dat2 <- with(dat, data.frame(x=days.rel[-len], xend=days.rel[-1],
                             y=hrs.away[-len], yend=hrs.away[-1],
                             type=factor(as.integer(type[-1]))))

ggplot() +
  geom_point(data=dat, aes(x=days.rel, y=hrs.away)) +
  geom_segment(data=dat2, aes(x=x, xend=xend, y=y, yend=yend, lty=type, size=type)) +
  scale_linetype_manual(values=2:1) +
  scale_size_manual(values=c(0.5,1)) +
  ylim(0, 4) + theme_bw()