Adjusting geom_bar (position="dodge") in ggplot

You can customise the dodging by specifying position = position_dodge(...).

ggplot (df, aes(x=z, y=value, fill=variable)) + 
  geom_bar (stat="identity", position = position_dodge(width = 0.5))

I solved it with the help of above, but further adjustment:

ggplot(df, aes(x=z, y=value, fill=variable)) + 
  geom_bar(stat="identity", position = position_dodge2(width = 0.5, preserve = "single", padding = -0.5))