library(reshape2)
library(ggplot2)

df = data.frame(cat = LETTERS[1:6], VAR1 = runif(6), VAR2 = runif(6), VAR3 = runif(6), VAR4 = runif(6))

head(df)
df_melted = melt(df, id.vars = 'cat')

head(df_melted)