Which part to plot: "both", "bottom", or "top". For backward compatibility, part also accepts the integer codes 2 ("both"), 0 ("bottom"), and 1 ("top").
ncol
Number of columns in facet layout.
num_xaxis
How to treat numeric column names on the x-axis.
"auto": use "log" if column names are numeric and
evenly spaced on a log scale with a range ratio >= 1000, otherwise
keep them as factor levels. "log" or "numeric": force
the corresponding scale. "character", "factor",
"keep", or FALSE: keep as character/factor.
1. Example data is from https://smear.avaa.csc.fi/download. It includes
particle number concentrations in SMEAR I Varrio forest.
2. Wickham, H. 2016. ggplot2: elegant graphics for data analysis.
Springer-Verlag New York.