使用新标签在 ggplot 中手动添加 x 轴？

Question

Hopefully this is a pretty simple question. I am trying to manually label the x-axis for a line graph (temperature) and bar graph (river discharge) with a shared x-axis and different y-axes, yet I have been consistently unsuccessful, and I really don't know why.

My first dataset (bar graph) looks like this:

And my second dataset (line graph) looks like this:

This is the script I wrote that gives me the following image:

p.dt <- ggplot(discharge, aes(x=date,y=discharge)) +
  geom_bar(stat="identity",width=1) +
  annotate("rect", xmin=1, xmax=152,ymin=0,ymax=850,alpha=.25) +
  geom_line(data = temp.ave, inherit.aes = FALSE, aes(x=num, y=average/0.03, group=1), size=2) +
  scale_y_continuous(sec.axis = sec_axis(~.*0.03, name = "Temperature (C)")) +
  theme_linedraw(base_size = 18) +
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(), 
        strip.text = element_text(face = "bold")) +
  theme(axis.text.x = element_blank(), axis.ticks = element_blank()) +
  labs(y = "Discharge (cfs)", x = "") 
  #ggtitle("USGS Gauge 09112200 Discharge and HOBO Temp")

print(p.dt)

Okay. So, I would like to manually label the x-axis every fourth month (example: 11/1/17 to "Nov 2017"), and the data points are shared between the two datasets. I have been adding a single line of scale_x_discrete after adding the temperature layer as a second axis with no avail:

p.dt <- ggplot(discharge, aes(x=date,y=discharge)) +
  geom_bar(stat="identity",width=1) +
  annotate("rect", xmin=1, xmax=152,ymin=0,ymax=850,alpha=.25) +
  geom_line(data = temp.ave, inherit.aes = FALSE, aes(x=num, y=average/0.03, group=1), size=2) +
  scale_y_continuous(sec.axis = sec_axis(~.*0.03, name = "Temperature (C)")) +
  scale_x_discrete(labels = c("11/1/17" = "Nov 2017", "3/1/18" = "Mar 2018", "7/1/18" = "Jul 2018")) +
  theme_linedraw(base_size = 18) +
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(), 
        strip.text = element_text(face = "bold")) +
  theme(axis.text.x = element_blank(), axis.ticks = element_blank()) +
  labs(y = "Discharge (cfs)", x = "") 
  #ggtitle("USGS Gauge 09112200 Discharge and HOBO Temp")

print(p.dt)

I imagine this has something to do with my two y-axes and two separate datasets. Thoughts?

Thank you in advance,

J

Answer 1

You could perhaps have the column date as Posixct and use:

scale_x_datetime(labels = date_format("%m-%Y"), breaks = '4 months') +

Answer 2

Another option, following the examples here , you can replace scale_x_discrete with

scale_x_date(date_breaks = "4 month", date_labels = "%m-%Y")