AF_combine: AF Combination of P-values
In songbiostat/MiAF: Microbiome Adaptive Fisher Test

This function combines p-values using adaptive Fisher method.

1	AF_combine(p, weight = 1, log = TRUE)

`p`	P-values to be combined. A matrix with dimenstions K by B. If an object of p-values from perm.mar.cov() is used, K is the number of OTUs, and B is the number of permutataion plus 1. The first column is observed marginal p-values, and the rest columns are p-values for permutation.
`weight`	Weights given to the p-values.
`log`	Indicator of whether p-values are on the log scale.

A list containing the following elements:

`pvalue`	P-value of AF statistic for observed sample (the first element) and all permuted samples.
`which.selected`	The index of features to be selected.