quick-and-dirty implementation to find the overlap area of the convex hulls of vowel measurements

voach.R

library(phonR)  # convexHullArea
library(sp)     # SpatialPolygons, etc
library(rgeos)  # gIntersection
data(indoVowels)
female_two <- indo[indo$subj == "F02",]
by_vowel <- split(female_two, female_two$vowel)
hull_indices <- sapply(by_vowel, function(df) with(df, chull(f1, f2)))
hulls <- sapply(names(by_vowel), function(v) by_vowel[[v]][hull_indices[[v]],],
                simplify=FALSE)
matrices <- sapply(hulls, function(df) as.matrix(df[,c("f1", "f2")]))
closed_mats <- sapply(matrices, function(m) rbind(m, m[1,]))
polygons <- sapply(closed_mats, Polygon, hole=FALSE)
polygon_lists <- sapply(names(polygons), function(i) Polygons(polygons[i], ID=i))
spatial_polygons <- sapply(names(polygon_lists), function(i) SpatialPolygons(polygon_lists[i]))
cmbns <- combn(names(by_vowel), 2)
overlap <- apply(cmbns, 2, function(i) gIntersection(spatial_polygons[[i[1]]],
                                                     spatial_polygons[[i[2]]]))
names(overlap) <- apply(cmbns, 2, paste, collapse="-")
overlap_area <- sapply(overlap, function(i) if (is.null(i)) {0} else {i@polygons[[1]]@area})
hull_area <- with(indo, convexHullArea(f1, f2, group=vowel))
voach <- sapply(names(overlap_area), function(i) {
    v <- strsplit(i, '-', fixed=TRUE)[[1]]
    min(hull_area[v]) / overlap_area[[i]]
})

Thanks for your replies. I will try it this weekend and hopefully report back my victory on Monday!