Center Y axis on 0 in geom_boxplot()

[bioinfguru]

Hello all,

EDIT: I can see I've not done this quite the way it should be done to produce an RLE plot (i.e. logging, and median substraction). I will be editing this.

I am producing EDA plots to check normalisation. I would like to center the y-axis on zero for the boxplots in my plot. I can do it by subtracting the median of medians from all values, but is there a one-line ggplot2 or other base function/method/argument that does it?

Data structure:

> dds_normalised_counts
# A tibble: 361,422 × 2
   sample count
    <dbl> <dbl>
 1      1  14.0
 2      5  14.2
 3      6  14.7
 4      8  14.5
 5      9  15.1
 6     10  15.1
 7     17  14.7
 8     18  14.7
 9     19  14.8
10     20  14.0
# ℹ 361,412 more rows
# ℹ Use `print(n = ...)` to see more rows

Code:

# get median of medians
median_of_medians <- dds_normalised_counts %>% 
  group_by(sample) %>%
  summarize(median = median(count, na.rm=TRUE)) %>%
  pull(median) %>%
  median()

# subtract from all values
dds_normalised_counts <- dds_normalised_counts %>%
  mutate(centered = count-median_of_medians)

# plot
ggplot(dds_normalised_counts, (aes(x = as.factor(sample), y = centered))) +
  geom_boxplot(outliers = FALSE, fill = "powderblue") + 
  xlab('sample') +
  ylab('count') + 
  labs(title = "VST Normalised Counts") + 
  theme_bw()+
  theme(
    panel.grid.major = element_blank(),
    panel.grid.minor = element_blank(),
    strip.background = element_rect()
  )

Without centering:

With centering:

Thanks in advance,
Kenneth