Plot observed densities
# S3 method for obs
plot(x, ..., dens_2 = NA, dens_3 = NA, time_unit = NA, combined = TRUE)
input
arguments passed on to the function
density 2 (if any). By default, `NA`.
density 3 (if any). By default, `NA`.
x-axis label of the output
whether to combine the two plots. By default, TRUE. If TRUE, then the plot function produces one ggplot object. If FALSE, three objects (two ggplot and one dataframe) will be produced.