Ggplot, Drawing Line Between Points Across Facets

ggplot, drawing line between points across facets

Updated to ggplot2 V3.0.0

You could do this, but turning clip off might have unwanted consequences,

library(ggplot2)
df <- data.frame(y=c(1,2,3),x=1,Set=LETTERS[1:3])
p <- ggplot(df,aes(x,y)) + 
  theme_bw() + theme(legend.position=c(.01,.99),legend.justification=c(0,1)) + 
  geom_point(aes(fill=Set),color="black",shape=21,size=3) + 
  facet_grid(~Set) + 
  xlim(1,5) 

gb <- ggplot_build(p)
g <- ggplot_gtable(gb)

library(gtable)
library(grid)
# ggplot2 doesn't use native units in data space
# instead, the data is rescaled to npc, i.e from 0 to 1
# so we need to use the build info to convert from data to [0,1]
ranges <- gb$layout$panel_params
data2npc <- function(x, range) scales::rescale(c(range, x), c(0,1))[-c(1,2)]

start <- c(data2npc(1, ranges[[1]][["x.range"]]), 
           data2npc(1, ranges[[1]][["y.range"]]))

end <- c(data2npc(1, ranges[[3]][["x.range"]]), 
           data2npc(3, ranges[[3]][["y.range"]]))
# starting position in the first panel
g <- gtable_add_grob(g, moveToGrob(start[1],start[2]), 
                     t = 8, l = 5)
# draw line to end position in last panel
g <- gtable_add_grob(g, lineToGrob(end[1],end[2]), 
                     t = 8, l = 9, z=Inf)
# turn clip off to see the line across panels
g$layout$clip <- "off"
grid.newpage()
grid.draw(g)

ggplot, drawing multiple lines across facets

Updated to ggplot2 V3.0.0

In the simple scenario where panels have common axes and the lines extend across the full y range you can draw lines over the whole gtable cells, having found the correct npc coordinates conversion (cf previous post, updated because ggplot2 keeps changing),

library(ggplot2)
library(gtable)
library(grid)

dat <- data.frame(x=rep(1:10,2),y=1:20+rnorm(20),z=c(rep("A",10),rep("B",10)))

p <- ggplot(dat,aes(x,y)) + geom_point() + facet_grid(z~.) + xlim(0,10)
pb <- ggplot_build(p)
pg <- ggplot_gtable(pb)


data2npc <- function(x, panel = 1L, axis = "x") {
  range <- pb$layout$panel_params[[panel]][[paste0(axis,".range")]]
  scales::rescale(c(range, x), c(0,1))[-c(1,2)]
}


start <- sapply(c(4,8), data2npc, panel=1, axis="x")

pg <- gtable_add_grob(pg, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=7, b=9, l=5)

grid.newpage()
grid.draw(pg)

ggplot: clipping lines between facets

library(grid)
library(gtable)

# Starting from your plot `p`
gb <- ggplot_build(p)
g <- ggplot_gtable(gb)

# Get position of y-axis tick marks
ys <- gb$layout$panel_ranges[[1]][["y.major"]]


# Add segments at these positions
# subset `ys` if you only want to add a few
# have a look at g$layout for relevant `l` and `r` positions
g <- gtable_add_grob(g, segmentsGrob(y0=ys, y1=ys, 
                                     gp=gpar(col="red", lty="dashed")), 
                     t = 7, l = 4, r=8)

grid.newpage()
grid.draw(g)

see ggplot, drawing multiple lines across facets for how to rescale values for more general plotting. ie

data2npc <- function(x, panel = 1L, axis = "x") {
  range <- pb$layout$panel_ranges[[panel]][[paste0(axis,".range")]]
  scales::rescale(c(range, x), c(0,1))[-c(1,2)]
}

start <- sapply(c(4,6,8), data2npc, panel=1, axis="y")

g <- gtable_add_grob(g, segmentsGrob(y0=start, y1=start),
                      t=7, r=4, l=8)

ggplot, drawing lines across multiple facets (x axis is date)

I have figured out my own answer!

The key is in changing t, b, and l in gtable_add_grob:

plot.g <- gtable_add_grob(plot.g, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=7, b=13,l=7)

Although, it seems to me to be trial and error to identify the correct values of t,b, and l.

New code:

library(ggplot2)
library(gtable)
library(grid)

data<-data.frame(Date=rep(seq(as.Date("2018-09-22","%Y-%m-%d"),
                              as.Date("2019-06-19","%Y-%m-%d"),
                              by=30),9),
                 Station=c(rep("A",30),rep("B",30),rep("C",30)),
                 Description=rep(c(rep("Var1",10),rep("Var2",10),
                                   rep("Var3",10)),3),
Data=c(seq(1,10,by=1),seq(500,800,length.out=10),seq(30,90,length.out=10),                seq(5,19,length.out=10),seq(450,1080,length.out=10),seq(20,60,length.out=10),                     seq(2,15,length.out=10),seq(600,750,length.out=10),seq(80,25,length.out=10)))

plot<-ggplot(data,aes(x=Date,y=Data,color=as.factor(Station)))+
  geom_line(size=1)+
  facet_grid(Description~.,scales="free_y",switch="y")+
  xlab("")+
  ylab("")+
  theme(panel.background=element_blank(),
        panel.grid.major.y=element_line(color="grey80",
                                        size=0.25),
        panel.grid.major.x=element_blank(),
        axis.line=element_line(color="black"),
        strip.placement="outside",
        strip.background=element_blank(),
        legend.position="top",
        legend.key=element_blank(),
        legend.title=element_blank())
plot
plot.b<-ggplot_build(plot)
plot.g<-ggplot_gtable(plot.b)
data2npc <- function(x, panel = 1L, axis = "x") {
  range <- plot.b$layout$panel_params[[panel]][[paste0(axis,".range")]]
  scales::rescale(c(range, x), c(0,1))[-c(1,2)]
}
start <- sapply(as.Date("2018-10-10","%Y-%m-%d"), data2npc, panel=1, axis="x")
plot.g <- gtable_add_grob(plot.g, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=7, b=13,l=7)

grid.newpage()
grid.draw(plot.g)

And new resulting plot

Connect multiple points across multiple facets with a dashed line

Note: it may not make sense to connect the lines between the chromosomes.

But here is one way, by avoiding facets:

library(dplyr)
df2 <- df %>% 
  mutate(chromosome = factor(chromosome, c(1, 2, 4, 5, 12, 16, 'X'))) %>% 
  arrange(chromosome, start.coordinate)
chromosome_positions <- df2 %>% 
  group_by(chromosome) %>% 
  summarise(start = first(start.coordinate), end = last(start.coordinate)) %>% 
  mutate(
    size = end - start,
    new_start = cumsum(lag(size, default = 0)),
    new_end = new_start + size
  )
df3 <- df2 %>% 
  left_join(chromosome_positions, 'chromosome') %>% 
  mutate(new_x = start.coordinate + (new_start - start))

ggplot(df3, aes(x=new_x,y=per.found, group=copy.number.type, color=copy.number.type))+
  geom_rect(
    aes(xmin = new_start, xmax = new_end, ymin = -Inf, ymax = Inf, fill = chromosome), 
    chromosome_positions, inherit.aes = FALSE, alpha = 0.3
  ) +
  geom_line() +
  geom_point() +
  geom_text(
    aes(x = new_start + 0.5 * size, y = Inf, label = chromosome),
    chromosome_positions, inherit.aes = FALSE, vjust = 1
  ) + 
  scale_fill_manual(values = rep(c('grey60', 'grey90'), 10), guide = 'none') +
  scale_x_continuous(expand = c(0, 0))

Draw lines between two facets in ggplot2

In order to achieve that, you have to set the margins inside the plot to zero. You can do that with expand=c(0,0). The changes I made to your code:

• When you use scale_y_continuous, you can define the axis label inside that part and you don't need a seperarate ylab.
• Changed colour=I("black") to colour="black" inside geom_line.
• Added expand=c(0,0) to scale_x_continuous and scale_y_continuous.

The complete code:

ggplot(data=df, aes(x=t, y=values)) +
  geom_line(colour="black") +
  geom_point(data=points, aes(x = x, y = y), colour="green") +
  facet_grid(type ~ ., scales="free") +
  scale_x_continuous("t", expand=c(0,0)) +
  scale_y_continuous("Log values", trans="log10", expand=c(0,0)) +
  theme(axis.text.x=element_text(angle=90, vjust=0.5), panel.margin=unit(0, "lines"))

which gives:

---

Adding lines can also be done with geom_segment. Normally the lines (segments) will appear in both facets. If you want them to appear between the two facets, you will have to restrict that in data parameter:

ggplot(data=df, aes(x=t, y=values)) +
  geom_line(colour="black") +
  geom_segment(data=df[df$type=="Bytes",], aes(x=10, y=0, xend=200, yend=0), colour="green", size=2) +
  geom_segment(data=df[df$type=="Bytes",], aes(x=300, y=0, xend=350, yend=0), colour="green", size=1) +
  facet_grid(type ~ ., scales="free") +
  scale_x_continuous("t", expand=c(0,0)) +
  scale_y_continuous("Log values", trans="log10", expand=c(0,0)) +
  theme(axis.text.x=element_text(angle=90, vjust=0.5), panel.margin=unit(0, "lines"))

which gives:

---

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