making a presence/absence timeline in r for multiple y objects - r

Question

This is my first time using SO and I am an R newbie; sorry if this is a little basic or unclear (or if the question has already been answered... I'm struggling with coding and need pretty specific answers to understand)
I would like to produce an image similar to this one:
Except I would like it to be oriented horizontally on a timeline, and with two vertical lines drawn from the x-axis.
I can set the data up simply, and there are only two variables - date and Tag.
Tag Date
1 1 1/1/2014
2 3 1/1/2014
3 1 1/3/2014
4 2 1/3/2014
5 3 1/3/2014
6 5 1/3/2014
7 2 1/4/2015
8 3 1/4/2015
9 4 1/4/2015
10 6 1/4/2015
11 1 1/5/2014
12 2 1/5/2014
13 4 1/5/2014
14 6 1/5/2014
15 1 1/6/2014
16 2 1/6/2014
17 3 1/6/2014
18 4 1/6/2014
19 6 1/6/2014
20 2 1/7/2014
21 4 1/7/2014
22 1 1/8/2014
23 2 1/8/2014
24 6 1/8/2014
Here is a drawn image of what I would like to accomplish:
To recap - I want to take this data, which shows the dates of detection of animals at a certain location and plot it on a timeline with two vertical lines on two dates. If an animal (say, tag 2) was detected on consecutive days, I would like to connect those dates with a line, and if the detection happened without detection on consecutive days, a simple dot will suffice. I imagine the y-axis is stacked with each individual Tag, and the x-axis is a date scale - for each date, if A tag ID was detected, then its corresponding x,y coordinate will be marked; if a tag was not detected on a certain date; the corresponding x,y coordinate will remain blank.
Here's a follow-up question:
I want to add a shaded background to some of the dates. I figured that I can use this using geom_rect, but i keep getting the following error:
Error: Invalid input: date_trans works with objects of class Date only
using the code you wrote, this is what I have added to receive the error:
geom_rect(aes(xmin=16075, xmax=16078, ymin=-Inf, ymax=Inf), fill="red", alpha=0.25)
this code will plot, but is not transparent, and so becomes fairly useless:
geom_rect(xmin=16075, xmax=16078, ymin=-Inf, ymax=Inf)

Answer 1

You first need to change your date format into Date. Then you need to figure out if dates are consecutive. And finally you need to plot them. Below is a possible solution using the packages dplyr and ggplot2.
# needed packages
require(ggplot2)
require(dplyr)
# input your data (changed to 2014 dates)
dat <- structure(list(Tag = c(1L, 3L, 1L, 2L, 3L, 5L, 2L, 3L, 4L, 6L, 1L, 2L, 4L, 6L, 1L, 2L, 3L, 4L, 6L, 2L, 4L, 1L, 2L, 6L), Date = structure(c(1L, 1L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 5L, 6L, 6L, 7L, 7L, 7L), .Label = c("1/1/2014", "1/3/2014", "1/4/2014", "1/5/2014", "1/6/2014", "1/7/2014", "1/8/2014"), class = "factor")), .Names = c("Tag", "Date"), class = "data.frame", row.names = c(NA, -24L))
# change date to Date format
dat[, "Date"] <- as.Date(dat[, "Date"], format='%m/%d/%Y')
# adding consecutive tag for first day of cons. measurements
dat <- dat %>% group_by(Tag) %>% mutate(consecutive=c(diff(Date), 2)==1)
# plotting command
ggplot(dat, aes(Date, Tag)) + geom_point() + theme_bw() +
geom_line(aes(alpha=consecutive, group=Tag)) +
scale_alpha_manual(values=c(0, 1), breaks=c(FALSE, TRUE), guide='none')