beta2-class is used to store the results of beta diversity analysis,
including results for drawing and comparing differences between groups.
metaA data frame storing basic elements for visualization.
resultA character of pairwise comparison results.
tempA character vector of the difference comparison.
Users can construct a beta2-class through calc_beta2,
which can then be connected to nem_plot to visualize the results.
The constructor, calc_beta2; Class for storing single factor beta
diversity analysis, beta-class; Visualization function,
nem_plot.