To add a space to separate groups

Add a space in a boxplot

df <- data.frame(cntNorm2$id_1,
                 mean_WT_PBMC_2m,mean_WT_PBMC_24m,mean_WT_PBMC_28m,
                 mean_HD_PBMC_Young_F, mean_HD_PBMC_Young_M, mean_HD_PBMC_Old_F, mean_HD_PBMC_Old_M)


# add a fake column with extremely large value
df$empty <- c(rep(100000,nrow(df)))


# turns outliers (> upper quatile * 5) into NAs
filter_lims <- function(x){
  u <- boxplot.stats(x)$stats[5] * 5

  for (i in 1:length(x)){
    x[i] <- ifelse(x[i]<u, x[i], NA)
  }
  return(x)
}


m_df <-  reshape2::melt(df)
m_df <- m_df %>%
  group_by(id) %>%
  mutate(value2 = filter_lims(value))  # too high values removed from data
  

ggplot(m_df, ...)