ggplot2 displaying unlabeled tick marks between labeled tick marks

Question

I've been having issues displaying minor tick marks on my histogram plot. I've tried the idea of plotting unlabeled major tick marks, but the tick marks wouldn't display. My code is pretty cumbersome and probably has some redundant lines. Any help would be appreciated.

ggplot(data=Shrimp1, aes(Shrimp1$Carapace.Length))+
geom_histogram(breaks=seq(3.5, 25, by=0.1),
             col="black",
             fill="gray", 
             alpha=1)+ 

 labs(title="Total Female Carapace Length")+
 labs(x="Carapace Length (mm)", y="# of Shrimp")+
  xlim(c(3.5, 25))+
  theme_bw()+
scale_y_continuous(expand = c(0,0),
                     limits = c(0,200))+
scale_x_continuous(breaks=seq(2.5,25,2.5))+

theme(axis.text.x=element_text(size=30,angle=45,hjust=1))+
  theme(plot.title=element_text(size=30, hjust=0.5))+
  theme(axis.text=element_text(size=30, color = "black"), 
        axis.title=element_text(size=30,face="bold"))+
  theme(panel.grid.major=element_line(colour="white"), 
        panel.grid.minor = element_line(colour = "white"))+
  theme(panel.border=element_blank())+
  theme(axis.ticks.x = (element_line(size=2)), 
        axis.ticks.y=(element_line(size=2)))+
  theme(axis.ticks.length=unit(.55, "cm"))+
  theme(panel.border=element_blank(), axis.line.x=element_line(colour="black"),
        axis.line.y=element_line(colour="black"))

Major ticks are present but I need minor ticks between them at intervals of 0.1

Can't you just change your `scale_x_continuous(breaks=seq(2.5,25,2.5))` to `scale_x_continuous(breaks=seq(2.5,25,0.1))`? — acylam, Sep 25 '17 at 19:27
Labels are then created for every increment. The x-axis is then crowded with numbers rather than label-less tick marks. — Spooner, Sep 25 '17 at 19:33
@Ian Kent's answer is great, but you can also see these answers: https://stackoverflow.com/questions/34533472/insert-blanks-into-a-vector-for-e-g-minor-tick-labels-in-r/34533473#34533473, https://stackoverflow.com/questions/14490071/adding-minor-tick-marks-to-the-x-axis-in-ggplot2-with-no-labels — acylam, Sep 25 '17 at 20:46

score 6 · Answer 1 · edited Jul 28 '20 at 11:20

I don't think you can add ticks to minor breaks, but you can have unlabeled major ticks, as you were thinking, by labeling them explicitly in scale_x_continuous. You can set the "minor" tick labels to blank using boolean indexing with mod (%%).

Similarly, you can set the tick sizes explicitly in theme if you want the "minor" ticks to be a different size.

set.seed(5)
df <- data.frame(x = rnorm(500, mean = 12.5, sd = 3))

breaks <- seq(2.5, 25, .1)

labels <- as.character(breaks)
labels[!(breaks %% 2.5 == 0)] <- ''
tick.sizes <- rep(.5, length(breaks))
tick.sizes[(breaks %% 2.5 == 0)] <- 1

df %>% 
  ggplot(aes(x)) +
  geom_histogram(binwidth = .1, color = 'black', fill = 'gray35') +
  scale_x_continuous(breaks = breaks, labels = labels, limits = c(2.5,25)) +
  theme_bw() +
  theme(panel.grid = element_blank(), 
        axis.ticks.x = element_line(size = tick.sizes))

Also as you might notice from my code, you can just call theme() once and put all the theme modifications into that one call.

Plot

ggplot2 displaying unlabeled tick marks between labeled tick marks

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