Order dataframe by two columns (secondary sort)

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examples/data-frames/order_dataframe_by_two_conditions.R

df = data.frame(A=c(2, 1, 1, 3), B=c(2, 4, 3, 1))
df
df[order(df$A),]
df[order(df$B),]
df[order(df$A, df$B),]