Adding a second y axis in R

Question

I am envisioning to use the following dataset to create a plot that combines a clustered bar chart and line chart with the following data:

structure(list(X = 1:14, ORIGIN = c("AUS", "AUS", "DAL", "DAL", 
"DFW", "DFW", "IAH", "IAH", "OKC", "OKC", "SAT", "SAT", "SHV", 
"SHV"), DEST = structure(c(1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 
2L, 1L, 2L, 1L, 2L), .Label = c("ATL", "SEA"), class = "factor"), 
    flight19.x = c(293L, 93L, 284L, 93L, 558L, 284L, 441L, 175L, 
    171L, 31L, 262L, 31L, 175L, 0L), flight19.y = c(5526L, 5526L, 
    6106L, 6106L, 23808L, 23808L, 15550L, 15550L, 2055L, 2055L, 
    3621L, 3621L, 558L, 558L)), row.names = c(NA, -14L), class = "data.frame")

In Excel, the chart I am envisioning looks something like this:

I have already tried to used the sec.axis function to generate a second axis. However, the outcome looks like the line plot still uses the first y-axis instead of the second axis:

p1 <- ggplot()+
  geom_bar(data = flight19, aes(ORIGIN, flight19.x, fill = DEST),stat = "identity", position = "dodge" )+
  scale_fill_viridis(name = "Destinations", discrete = TRUE)+
  labs(y= "Operation Counts", x = "Airports")


p2 <- p1 + geom_line(data = flight19, aes(as.character(ORIGIN), flight19.y, group = 1))+
  geom_point(data = flight19, aes(as.character(ORIGIN), flight19.y, group = 1))+
  scale_y_continuous(limit = c(0,600),sec.axis = sec_axis(~.*75/10, name = "Total Monthly Operations"))

The plot shows the warning below:

Warning messages:
1: Removed 12 row(s) containing missing values (geom_path). 
2: Removed 12 rows containing missing values (geom_point).

And the codes produce the plot below:

Could someone teach me how to let the line plot corresponds to the second axis? Thanks so much in advance.

Does this answer your question? [ggplot with 2 y axes on each side and different scales](https://stackoverflow.com/questions/3099219/ggplot-with-2-y-axes-on-each-side-and-different-scales) — A. Suliman, Jun 19 '20 at 18:08

score 0 · Accepted Answer · answered Jun 19 '20 at 18:06

Find a suitable transformation factor, here I used 50 just to get nice y-axis labels

#create x-axis 
flight19$x_axis <- paste0(flight19$ORIGIN,'\n',flight19$DEST)

# The transformation factor
#transf_fact <- max(flight19$flight19.y)/max(flight19$flight19.x)
transf_fact <- 50

ggplot(flight19, aes(x = x_axis)) +
  geom_bar(aes(y = flight19.x),stat = "identity", fill = "blue") +
  geom_line(aes(y = flight19.y/transf_fact,group=1), color = "orange") + 
  scale_y_continuous(name = "Operation Counts",
                     limit = c(0,600),
                     breaks = seq(0,600,100), 
                     sec.axis = sec_axis(~ (.*transf_fact), 
                                         breaks = function(limit)seq(0,limit[2],5000),
                                         labels = scales::dollar_format(prefix = "$",suffix = " k",scale = .001),
                                         name = "Total Monthly Operations")) + 
  xlab("Airports") + 
  theme_bw()

Adding a second y axis in R

1 Answers1