Nudge ggplot text based on value [duplicate]

Question

How would I nudge text based on value:

E.g.,

library(ggplot2)
theme_set(theme_bw())  

# Data Prep
data("mtcars")  # load data
mtcars$`car name` <- rownames(mtcars)  # create new column for car names
mtcars$mpg_z <- round((mtcars$mpg - mean(mtcars$mpg))/sd(mtcars$mpg), 2)  # compute normalized mpg
mtcars$mpg_type <- ifelse(mtcars$mpg_z < 0, "below", "above")  # above / below avg flag
mtcars <- mtcars[order(mtcars$mpg_z), ]  # sort
mtcars$`car name` <- factor(mtcars$`car name`, levels = mtcars$`car name`)  # convert to factor to retain sorted order in plot.

# Diverging Barcharts
ggplot(mtcars, aes(x=`car name`, y=mpg_z, label=mpg_z)) + 
  geom_bar(stat='identity', aes(fill=mpg_type), width=.5)  +
  scale_fill_manual(name="Mileage", 
                    labels = c("Above Average", "Below Average"), 
                    values = c("above"="#00ba38", "below"="#f8766d")) + 
  geom_text(size=2, nudge_y = 0.1) +
  labs(subtitle="Normalised mileage from 'mtcars'", 
       title= "Diverging Bars") + 
  coord_flip()

Currently, text shows on top of negative bars:

I'd like to nudge it to the left only for these bars, to the right for positive bars.

Example source

Answer 1

We may use, e.g.,

geom_text(size = 2, nudge_y = -0.1 + 0.2 * (mtcars$mpg_z > 0))

or

geom_text(size = 2, nudge_y = ifelse(mtcars$mpg_z > 0, 0.1, -0.1))

to construct a vector of nudge_y values. This gives

Answer 2

Here, instead of using nudge_y I just manually add (or subtract) a fixed value to y in geom_text depending on the sign of mpg_z, as determined by the aptly named function sign. The only line that differs from your example is geom_text(size=2, aes(y = mpg_z + 0.1 * sign(mpg_z)))

library(ggplot2)
theme_set(theme_bw())  

# Data Prep
data("mtcars")  # load data
mtcars$`car name` <- rownames(mtcars)  # create new column for car names
mtcars$mpg_z <- round((mtcars$mpg - mean(mtcars$mpg))/sd(mtcars$mpg), 2)  # compute normalized mpg
mtcars$mpg_type <- ifelse(mtcars$mpg_z < 0, "below", "above")  # above / below avg flag
mtcars <- mtcars[order(mtcars$mpg_z), ]  # sort
mtcars$`car name` <- factor(mtcars$`car name`, levels = mtcars$`car name`)  # convert to factor to retain sorted order in plot.

# Diverging Barcharts
ggplot(mtcars, aes(x=`car name`, y = mpg_z, label=mpg_z)) + 
  geom_bar(stat='identity', aes(fill=mpg_type), width=.5)  +
  scale_fill_manual(name="Mileage", 
                    labels = c("Above Average", "Below Average"), 
                    values = c("above"="#00ba38", "below"="#f8766d")) + 
  geom_text(size=2, aes(y = mpg_z + 0.1 * sign(mpg_z))) +
  labs(subtitle="Normalised mileage from 'mtcars'", 
       title= "Diverging Bars") + 
  coord_flip()

^{Created on 2019-02-05 by the reprex package (v0.2.1)}