How to order x axis based on y axis values (in decreasing order)

r ggplot2

Maybe this is what you are looking for. To order the bars in decreasing order without grouping by allele you could add a helper variable via interaction which could then be mapped on x.

To only show the allele on the x axis I make use of a custom labels function in scale_x_discrete and use an underscore as separator in interaction.

library(ggplot2)

df$subject <- factor(df$subject, levels =c("her", "xan", "las", "reth"))
df$pososto = as.numeric(df$pososto)

df$x <- interaction(df$allele, df$subject, sep = "_")

ggplot(df, aes(x = reorder(x, -pososto), y = pososto, fill = subject)) + 
  geom_col(position = "dodge") +
  scale_x_discrete(labels = ~ gsub("^(.*?)_.*$", "\\1", .x)) +
  scale_fill_manual(values=c("#696969","#778899","#A9A9A9","#CCCCFF"))+
  theme_bw(base_size = 9) +
  geom_hline(yintercept = 0, colour = "black") +
  theme(axis.text.x = element_text(angle = 60, hjust = 1))

Are you looking for such a solution?

library(tidyverse)
df %>% 
  arrange(allele, pososto, subject) %>% 
  group_by(allele) %>% 
  mutate(id=row_number()) %>%
  mutate(subject = fct_reorder(allele, id)) %>%
  ggplot(aes(x = allele, y = pososto, fill=factor(id))) + 
  geom_col(position=position_dodge())+
  scale_x_discrete(limits = (unique(df$allele))) +
  theme_bw(base_size = 9) +
  geom_hline(yintercept = 0, colour = "black") +
  scale_fill_manual(values=c("#696969","#778899","#A9A9A9","#CCCCFF"), labels = c("her", "reth", "las", "xan"))+
  theme(axis.text.x = element_text(angle = 60, hjust = 1))

data:

df <- structure(list(allele = c("Ak24:02", "Ak24:02", "Ak24:02", "Ak24:02", 
"Ak02:01", "Ak02:01", "Ak02:01", "Ak02:01", "Ak01:01", "Ak01:01", 
"Ak01:01", "Ak01:01", "Ak11:01", "Ak11:01", "Ak11:01", "Ak11:01", 
"Ak03:01", "Ak03:01", "Ak03:01", "Ak03:01", "Ak32:01", "Ak32:01", 
"Ak32:01", "Ak32:01"), subject = c("her", "reth", "las", "xan", 
"her", "reth", "las", "xan", "her", "reth", "las", "xan", "her", 
"reth", "las", "xan", "her", "reth", "las", "xan", "her", "reth", 
"las", "xan"), pososto = c(6.2076749, 0, 14.3529412, 0, -0.7751938, 
0, -0.7751938, 0, 5.0666604, 0, 0, 11.944798, 0, 0, 9.7559913, 
6.0631187, -12.4022258, -1.3476446, 13.1983584, 17.1626014, 0, 
-13.1511297, 14.7583726, -5.6592186)), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", 
"14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24"
))

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