How can I add horizontal lines between my vertical lines in ggplot?

Question

I have a dataframe new which looks like this:

> new
     group        date         relamount     average
1       1     2012-07-01       2.3498695     1.524178
2       1     2012-08-01       0.6984866     1.524178
3       2     2012-09-01       0.9079118     1.896867
4       2     2012-10-01       2.8858218     1.896867
5       3     2012-11-01       1.2406948     1.777372
6       3     2012-12-01       2.3140496     1.777372
7       4     2013-01-01       1.5904573     2.421820
8       4     2013-02-01       3.2531825     2.421820
9       5     2013-03-01       4.2962963     3.812503
10      5     2013-04-01       3.3287101     3.812503
11      6     2013-05-01       3.7698413     2.603770
12      6     2013-06-01       1.4376997     2.603770
13      7     2013-07-01       5.0687285     4.760392
14      7     2013-08-01       4.4520548     4.760392
15      8     2013-09-01       5.5063913     5.537038
16      8     2013-10-01       5.5676856     5.537038
17      9     2013-11-01       6.2686567     8.644863
18      9     2013-12-01      11.0210697     8.644863

I plot the data (date on x axis, relamount on y axis) and have new$group as vertical lines.

What I want:

Horizontal lines between the vertical lines based on new$average...so far tried to do it like this with geom_segment: I know I have to have a specific start and end point for geom_segment, but maybe I can also do it like this? As expected it didn't work.

seq <- seq(2, nrow(df1), by=2)  # points for vertical lines
ggplot(new, aes(date, relamount)) +          # plot data 
  geom_line() + 
  geom_vline(xintercept = new$date[seq])     # create vertical lines
  geom_segment(data = new, aes(x = new$group,    # create horiz. lines 
                               y = new$average, 
                            xend = new$group +1, 
                            yend = new$average))

So I just want to have the red lines (new$average) between the vertical lines.

Answer 1

library(ggplot2)

new = read.table(text = "
group        date         relamount     average
1       1     2012-07-01       2.3498695     1.524178
2       1     2012-08-01       0.6984866     1.524178
3       2     2012-09-01       0.9079118     1.896867
4       2     2012-10-01       2.8858218     1.896867
5       3     2012-11-01       1.2406948     1.777372
6       3     2012-12-01       2.3140496     1.777372
7       4     2013-01-01       1.5904573     2.421820
8       4     2013-02-01       3.2531825     2.421820
9       5     2013-03-01       4.2962963     3.812503
10      5     2013-04-01       3.3287101     3.812503
11      6     2013-05-01       3.7698413     2.603770
12      6     2013-06-01       1.4376997     2.603770
13      7     2013-07-01       5.0687285     4.760392
14      7     2013-08-01       4.4520548     4.760392
15      8     2013-09-01       5.5063913     5.537038
16      8     2013-10-01       5.5676856     5.537038
17      9     2013-11-01       6.2686567     8.644863
18      9     2013-12-01      11.0210697     8.644863
", header=T)

# get points for vertical lines
seq <- seq(2, nrow(new), by=2) 

ggplot() +    
  geom_line(data=new, aes(date, relamount, group=1)) +             # plot line of data points
  geom_vline(xintercept = as.numeric(new$date[seq])) +             # plot vertical lines
  geom_segment(data=new[seq,], aes(x=as.numeric(date)-2,           # plot horizontal lines (segments)
                                   xend=as.numeric(date), 
                                   y=average, 
                                   yend=average), col="red") +
  scale_x_discrete(breaks = new$date[seq], labels = new$date[seq]) # adjust x axis labels