Reorder bars in geom_bar ggplot2 by value

Question

Your code works fine, except that the barplot is ordered from low to high. When you want to order the bars from high to low, you will have to add a -sign before value:

ggplot(corr.m, aes(x = reorder(miRNA, -value), y = value, fill = variable)) + 
  geom_bar(stat = "identity")

which gives:

---

Used data:

corr.m <- structure(list(miRNA = structure(c(5L, 2L, 3L, 6L, 1L, 4L), .Label = c("mmu-miR-139-5p", "mmu-miR-1983", "mmu-miR-301a-3p", "mmu-miR-5097", "mmu-miR-532-3p", "mmu-miR-96-5p"), class = "factor"),
                         variable = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = "pos", class = "factor"),
                         value = c(7L, 75L, 70L, 5L, 10L, 47L)),
                    class = "data.frame", row.names = c("1", "2", "3", "4", "5", "6"))

Aside from what @Jaap answered, there are two other ways to order the plot:

1: By using desc argument for value:

ggplot(corr.m, aes(x = reorder(miRNA, desc(value)), y = value, fill = variable)) + 
   geom_bar(stat = "identity")

2: By releveling the miRNA factor and omitting reorder argument:

corr.m %>%
   arrange(desc(value)) %>%
   mutate(miRNA = factor(miRNA, levels = unique(miRNA))) %>% 
ggplot(aes(x = miRNA, y = value, fill = variable)) + 
   geom_bar(stat = "identity")