how to fix, Geom_point working but geom_line not working when graphing with 2 y graphs on ggplot?

Question

I'm trying to map 2 different sets of data on the same x-axis but with different y axis. This is what my dataframe (individual_dets) looks like

month      num_unique_tags     ave_temp    year     zone  

Jan             7                1.16       2016      2
Jan             7                1.16       2017      1
Feb             6                1.17       2018      1   
Feb             6                1.17       2018      2
Mar             1                2.0        2016      3
Jun             2                2.3        2016      4
Apr             1                2.0        2016      4
Apr             1                3.1

So the x axis is month, the left y-axis is num_unique_detections and the right y axis is ave_temp. When I plot with the following code.

ggplot(individual_dets, aes(x = month, y = num_unique_tags)) +
#Graph month * unique_dets
  geom_bar(aes(fill = zone), position = "dodge", stat = "identity") +
#Graph the temperature
  geom_point(mapping = aes(x = month, y = ave_temp), color = "black", data = individual_dets) +
#Make graph with 2 y axis
  scale_y_continuous(name = "Total Unique Detections", 
                     sec.axis = sec_axis(~ . -2/2, name = "Ave Temp")) +
  scale_fill_manual(values=c("#01579B", "#4FC3F7", "#ffa600", "#ff6361")) +
  ylim(0,8) +
  xlab("Month") +
  ylab("Total Unique Detections") +
#Facet wrap by year
  facet_wrap(~ year, scales = "free", nrow = 3, strip.position = "top") + 
  theme_bw() + 
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.background = element_blank(), axis.line = element_line(),

        strip.background =  element_rect(fill = NA, colour = NA), 
        strip.text =        element_text(size = 25),

        text = element_text(family = "sans", size = 24))

I get this picture

which is good except, I want the points to be a line... but when I use geom_line instead of geom_point using this code

ggplot(individual_dets, aes(x = month, y = num_unique_tags)) +
#graph the month * unique_dets
  geom_bar(aes(fill = zone), position = "dodge", stat = "identity") +
#Graph the temperature, but not showing up
  geom_line(mapping = aes(x = month, y = ave_temp), color = "black", data = individual_dets) +
#Make 2 different y axis
  scale_y_continuous(name = "Total Unique Detections", 
                     sec.axis = sec_axis(~ . -2/2, name = "Ave Temp")) +
#Hex codes to denote the zone
  scale_fill_manual(values=c("#01579B", "#4FC3F7", "#ffa600", "#ff6361")) +
  ylim(0,8) +
  xlab("Month") +
  ylab("Total Unique Detections") +
#Facet wrap by year
  facet_wrap(~ year, scales = "free", nrow = 3, strip.position = "top") + 
  theme_bw() + 
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.background = element_blank(), axis.line = element_line(),

        strip.background =  element_rect(fill = NA, colour = NA), 
        strip.text =        element_text(size = 25),

        text = element_text(family = "sans", size = 24))

I get an image with no line, just the bars

I'm not sure what I'm doing wrong, does anyone know how to fix this?

There's no year in the sample dataset. Please edit as shown [here](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). The question is currently not easy to reproduce — NelsonGon, Jan 26 '20 at 14:09

score 4 · Answer 1 · answered Jan 26 '20 at 15:54

You need to add group = 1 in the aes of your geom_line:

ggplot(df, aes(x = month, y = num_unique_tags))+
  geom_col(position = position_dodge(), aes(fill = as.factor(zone)))+
  geom_line(inherit.aes = FALSE, data = df,
             aes(x = month, y = ave_temp, group = 1), color = "black")+
  scale_x_discrete(limits = c("Jan","Feb","Mar","Apr","Jun"))+
  scale_y_continuous(limits = c(0,8), name = "Total Unique Detections", 
                     sec.axis = sec_axis(~ . -2/2, name = "Ave Temp")) +
  scale_fill_manual(name = "Zone",values=c("#01579B", "#4FC3F7", "#ffa600", "#ff6361"))+
  xlab("Month")+
  facet_wrap(~ year, scales = "free", nrow = 3, strip.position = "top") + 
  theme_bw() + 
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.background = element_blank(), axis.line = element_line(),
        strip.background =  element_rect(fill = NA, colour = NA), 
        strip.text =        element_text(size = 25),
        text = element_text(family = "sans", size = 24))

Is it what you are trying to achieve ?

PS: I made minor edition in your code to modify few points (geom_col instead of geom_bar(sat = "identity", delete ylab and set the y-axis name by adding the argument name in scale_y_continuous and the use of scale_x_discrete to order your x-axis by months)

Example Data

structure(list(month = c("Jan", "Jan", "Feb", "Feb", "Mar", "Jun", 
"Apr"), num_unique_tags = c(7L, 7L, 6L, 6L, 1L, 2L, 1L), ave_temp = c(1.16, 
1.16, 1.17, 1.17, 2, 2.3, 2), year = c(2016L, 2017L, 2018L, 2018L, 
2016L, 2016L, 2016L), zone = c(2L, 1L, 1L, 2L, 3L, 4L, 4L)), row.names = c(NA, 
-7L), class = c("data.table", "data.frame"), .internal.selfref = <pointer: 0x5600fdd64350>)

how to fix, Geom_point working but geom_line not working when graphing with 2 y graphs on ggplot?

1 Answers1