R ggplot2 sec_axis 指定輔助軸

sec_axis(
  trans = NULL,
  name = waiver(),
  breaks = waiver(),
  labels = waiver(),
  guide = waiver()
)

dup_axis(
  trans = ~.,
  name = derive(),
  breaks = derive(),
  labels = derive(),
  guide = derive()
)

derive()

p <- ggplot(mtcars, aes(cyl, mpg)) +
  geom_point()

# Create a simple secondary axis
p + scale_y_continuous(sec.axis = sec_axis(~ . + 10))


# Inherit the name from the primary axis
p + scale_y_continuous("Miles/gallon", sec.axis = sec_axis(~ . + 10, name = derive()))


# Duplicate the primary axis
p + scale_y_continuous(sec.axis = dup_axis())


# You can pass in a formula as a shorthand
p + scale_y_continuous(sec.axis = ~ .^2)


# Secondary axes work for date and datetime scales too:
df <- data.frame(
  dx = seq(
    as.POSIXct("2012-02-29 12:00:00", tz = "UTC"),
    length.out = 10,
    by = "4 hour"
  ),
  price = seq(20, 200000, length.out = 10)
 )

# This may useful for labelling different time scales in the same plot
ggplot(df, aes(x = dx, y = price)) +
  geom_line() +
  scale_x_datetime(
    "Date",
    date_labels = "%b %d",
    date_breaks = "6 hour",
    sec.axis = dup_axis(
      name = "Time of Day",
      labels = scales::time_format("%I %p")
    )
  )


# or to transform axes for different timezones
ggplot(df, aes(x = dx, y = price)) +
  geom_line() +
  scale_x_datetime("
    GMT",
    date_labels = "%b %d %I %p",
    sec.axis = sec_axis(
      ~ . + 8 * 3600,
      name = "GMT+8",
      labels = scales::time_format("%b %d %I %p")
    )
  )