find_hull: find hull function this function finds convex hull to draw...
In elittmann/erictools:

find hull function this function finds convex hull to draw polygons onto 2d pcoa plots per group

1	find_hull(df)

#first create ordination object (ord) using phyloseq
df <- as.data.frame(as.matrix(ord$vectors))
df$sample <- row.names(df)
df <- df %>%
  left_join(samp)

  hulls <- ddply(df,"area",fund_hull)

  #sample plot:
  df %>%
ggplot(aes(x=Axis.1,y=Axis.2)) +
  geom_point(size=4,aes(shape=day,color=group)) +
  theme_bw(base_size=18) +
  coord_equal() +
  geom_polygon(data=hulls,aes(fill=area),alpha=.2) +
  scale_color_manual(values=c("MNV"="steelblue2","Strep"="salmon")) +
  scale_fill_manual(values=c("MNV"="steelblue2","Strep"="salmon","1"="chartreuse4","-3"="gray33")) +
  xlab("Axis.1 [27.7%]") +
  ylab("Axis.2 [20.1%]") +
  ggtitle("PCoA Bray")