How to align the bars of a barplot with the X-axis using ggplot2 in R?

The bar plot is created with geom_bar function but there always exist some space between the bars and the X-axis labels. If we want to reduce that space or completely remove it we need to use scale_y_continuous function by defining expand argument for former and scale_y_continuous(expand=c(0,0)) for latter.

Example

ggplot(df,aes(x,y))+geom_bar(stat="identity")+scale_y_continuous(expand=c(0,0))

Output