r, ggplot2: Set x axis breaks with a fixed xlim

Question

I have the following data, which produces the following two plots stacked on top of each other:

#dataset 1
channel1 <- c("Channel 1", "Channel 1", "Channel 1", "Channel 1", "Channel 1")
start_time1 <- c(0.000, 9.719, 11.735, 14.183, 16.554)
stop_time1 <- c(9.719, 11.735, 14.183, 16.554, 18.482)
character1 <- c("A", "B", "C", "C", "B")

df1 <- data.frame(channel1, start_time1, stop_time1, character1)

#dataset1 plot
plot1 <- ggplot(df1, aes(fill = character1, color = character1)) +
  geom_rect(color = NA, aes(xmin = start_time1, xmax = stop_time1, ymin = -0.5, ymax = 0.5)) +
  scale_x_continuous(breaks = scales::pretty_breaks(n = 10)) +
  #xlim(0,20) +
  facet_grid(channel1 ~ .) +
  theme(axis.text.y=element_blank(),
        axis.ticks.y=element_blank() ) +
  scale_fill_manual(values=c("#F8766D", "#871282", "#ffe119", "#0072B2", "#00C094", "#00A9FF", "#C77CFF"))


#dataset 2
channel2 <- c("Channel 2", "Channel 2", "Channel 2", "Channel 2", "Channel 2")
start_time2 <- c(3, 3, 4, 7, 9)
stop_time2 <- c(3.5, 4, 6, 8, 11)
character2 <- c("A", "D", "C", "E", "B")

df2 <- data.frame(channel2, start_time2, stop_time2, character2)

#dataset2 plot

plot2 <- ggplot(df2, aes(fill = character2, color = character2)) +
  geom_rect(color = NA, aes(xmin = start_time2, xmax = stop_time2, ymin = -0.5, ymax = 0.5)) +
  scale_x_continuous(breaks = scales::pretty_breaks(n = 10)) +
  #xlim(0, 20) +
  facet_grid(channel2 ~ .) +
  theme(axis.text.y=element_blank(),
        axis.ticks.y=element_blank() ) +
  scale_fill_manual(values=c("#F8766D", "#871282", "#ffe119", "#0072B2", "#00C094", "#00A9FF", "#C77CFF"))

#combine plots
library(patchwork)

This is not good, because I want them to have same x-axis scale, which I can do by by using xlim instead of using scale_x_continuous, which produces plots that are more visually comparable:

#dataset 1
channel1 <- c("Channel 1", "Channel 1", "Channel 1", "Channel 1", "Channel 1")
start_time1 <- c(0.000, 9.719, 11.735, 14.183, 16.554)
stop_time1 <- c(9.719, 11.735, 14.183, 16.554, 18.482)
character1 <- c("A", "B", "C", "C", "B")

df1 <- data.frame(channel1, start_time1, stop_time1, character1)

#dataset1 plot
plot1 <- ggplot(df1, aes(fill = character1, color = character1)) +
  geom_rect(color = NA, aes(xmin = start_time1, xmax = stop_time1, ymin = -0.5, ymax = 0.5)) +
  #scale_x_continuous(breaks = scales::pretty_breaks(n = 10)) +
  xlim(0,20) +
  facet_grid(channel1 ~ .) +
  theme(axis.text.y=element_blank(),
        axis.ticks.y=element_blank() ) +
  scale_fill_manual(values=c("#F8766D", "#871282", "#ffe119", "#0072B2", "#00C094", "#00A9FF", "#C77CFF"))

But what if I want to customize the x-axis breaks? What if I want a break at every multiple of 2 instead of 5? I've looked around a lot, and haven't yet found a way to customize the breaks when the x-axis limit is fixed. scale_x_discrete() doesn't seem to do anything useful in this situation.

Any suggestions are most appreciated.

You can use breaks to scale it however you would like, for example, every 2 can be accomplished with scale_x_continuous(breaks = seq(0, 20, by = 2)). — Kat
– Kat, Commented Dec 4, 2023 at 1:07
that did change the breaks to multiples of two, the x-axis scales were still different — Wangana
– Wangana, Commented Dec 4, 2023 at 4:05

Zhiqiang Wang · Accepted Answer · 2023-12-04 04:52:28Z

1

Use scale_x_continuous() to specify breaks, and coord_cartesian(xlim = c(0, 20)) to define x limits for both plots.

plot1 <- ggplot(df1, aes(fill = character1, color = character1)) +
  geom_rect(color = NA, aes(xmin = start_time1, xmax = stop_time1, ymin = -0.5, ymax = 0.5)) +
  scale_x_continuous(breaks = seq(0, 20, 2)) +
  coord_cartesian(xlim = c(0, 20)) +
  facet_grid(channel1 ~ .) +
  theme(
    axis.text.y = element_blank(),
    axis.ticks.y = element_blank()
  ) +
  scale_fill_manual(values = c("#F8766D", "#871282", "#ffe119", "#0072B2", "#00C094", "#00A9FF", "#C77CFF"))

edited Dec 4, 2023 at 4:52

answered Dec 4, 2023 at 2:36

Zhiqiang Wang

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3 Comments

Wangana Over a year ago

for this specific example, yes that would work, and this is what I did originally, but, I have reasons to not do it this way, you can see another question I have here: stackoverflow.com/questions/77588625/… wherein I want to treat different sets of data differently with their own legends, thus warranting making each of them a separate plot

Zhiqiang Wang Over a year ago

Then, the solution would be the same: use scale_x_continuous(breaks = seq(0, 20, 2)) to define breaks, and coord_cartesian(xlim = c(0, 20)) to define x range for both plots.

Zhiqiang Wang Over a year ago

Revised my answer.

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