Question

Here is small example I want to plot (2 group and 2 subgroup, just for simplicity, however I might have n group and k subgroups).

grp <- c(  1,   1,   1,  1, 1,  1, 1, 1, 1,  2,2, 2, 2,2, 2, 2, 2, 2)
sgrp <- c("A", "A", "A", "A", "A",  "B", "B", "B", "B" ,  "A", "A", "A", "A",
  "B", "B", "B", "B", "B")
pos <- c(1.1, 2.1, 3.2, 4.1, 5.0,1.1, 2.0, 5.0, 6.2,1.0, 3.0, 4.1, 5.0,1.0,
 2.1, 3.01, 4.0, 5.02)
mydf <- data.frame (grp, sgrp, pos)
   grp sgrp  pos
1    1    A 1.10
2    1    A 2.10
3    1    A 3.20
4    1    A 4.10
5    1    A 5.00
6    1    B 1.10
7    1    B 2.00
8    1    B 5.00
9    1    B 6.20
10   2    A 1.00
11   2    A 3.00
12   2    A 4.10
13   2    A 5.00
14   2    B 1.00
15   2    B 2.10
16   2    B 3.01
17   2    B 4.00
18   2    B 5.02

Pos determines where ticks need to be in x axis. The central line (long line) starts from zero and ends at maximum position of grp + 1. Is is possible to make such graph ?

The resulting graph should something look like:

Edits:
Here is small trick I could do, but not achieved (not close) what I want to:

dgp <- c(0, 0, 0, 0, 0,  0.15, 0.15,0.15, 0.15 ,  0, 0, 0, 0,  
0.15, 0.15, 0.15, 0.15, 0.15)
mydf$dumv <- grp + dgp
plot(mydf$pos, mydf$dumv, pch = "+", ylab = "groups", xlab = "pos")

Update again:, got some idea but problems exists:

require(ggplot2)

grp <- c(  1,   1,   1,  1, 1,  1, 1, 1, 1,  2,2, 2, 2,2, 2, 2, 2, 2)
sgrp <- c("A", "A", "A", "A", "A",  "B", "B", "B", "B" ,  "A", "A", "A", "A",
  "B", "B", "B", "B", "B")
position <- c(1.1, 2.1, 3.2, 4.1, 5.0,1.1, 2.0, 5.0, 6.2,1.0, 3.0, 4.1, 5.0,1.0,
 2.1, 3.01, 4.0, 5.02)
mydf <- data.frame (grp, sgrp, pos)
dgp <- c(0, 0, 0, 0, 0,  0.15, 0.15,0.15, 0.15 ,  0, 0, 0, 0,
0.15, 0.15, 0.15, 0.15, 0.15)
mydf$barheight <- c(0.25)
mydf$group <- grp + dgp

ggplot(mydf) +
  geom_line(aes(position, factor(group), group = factor(group)),
            size = 2, colour = "purple") +
  geom_rect(aes(y = factor(group),
                xmin = position - 0.02,
                xmax = position + 0.02,
                ymin = group - barheight/2,
                ymax = group + barheight/2))

Problem: ….
(1) I can not make group non factor, the postion of rectangle are in wrong place, I want to put A, B next to each other while gap between 1 and 2.

(2) In real data, I will have more than two groups, can I automte calculation of dgp.

Answer 1

 plot(NULL, ylim=c(0,4), xlim=range(mydf$pos))
 abline(h=1:4 ,col=1:2 )
 with(mydf, segments(x0=pos, y0=as.numeric(interaction(mydf$grp, mydf$sgrp))-.2, 
                     y1=as.numeric(interaction(mydf$grp, mydf$sgrp))+.2,
                     col= mydf$grp, lty=as.numeric(mydf$sgrp)) )

(I’m not yet a ggplot user, so this is base graphics. You can tweak the ylim and add a ylab argument to properly label. You may want to also use yaxt="n" and axis() to label your groups and subgroups.)

Here’s an alternate setup using the interaction values to pick from a vector of vertical locations.

 plot(NULL, ylim=c(0.5,4.5), xlim=range(mydf$pos))
 with(mydf, segments(x0=pos, 
             y0=c(1.3,1.7,3.3,3.7)[as.numeric(interaction(mydf$grp, mydf$sgrp))]-.1, 
             y1=c(1.3,1.7,3.3,3.7)[as.numeric(interaction(mydf$grp, mydf$sgrp))]+.1, 
             col= mydf$sgrp, lty=as.numeric(mydf$grp)) )
abline(h=c(1.3,1.7,3.3,3.7) ,col= rep(1:2, each=2), lty=1:2,lwd=3)