d = data_frame()
e = data_frame()
for (i in rev(f)) {

  h = read_html(unz(z, i))
  d = rbind(d, data_frame(title = html_node(h, "h2") %>% html_text,
                          date = html_node(h, xpath = "//p[2]") %>% html_text))

  j = html_nodes(h, xpath = "//a") %>% html_attr("href")
  j = j[ grepl("^\\d{4}(.*)html(#\\w+)?$", j) ]

  if (length(j))
    e = rbind(e, data_frame(i, j))

}

e = filter(e, i != j)
e$i = gsub("(.*)\\.html(.*)?", "\\1", e$i)
e$j = gsub("(.*)\\.html(.*)?", "\\1", e$j)

e = apply(e, 1, function(x) paste0(sort(x), collapse = "_"))
e = as.data.frame(table(e))
e = data_frame(i = gsub("(.*)_(.*)", "\\1", e[, 1]),
               j = gsub("(.*)_(.*)", "\\2", e[, 1]),
               w = e[, 2])