calculate_arbolate_sum(x)

library(dplyr)
source(system.file("extdata", "walker_data.R", package = "nhdplusTools"))
catchment_length <- select(walker_flowline, COMID, AreaSqKM) %>%
  right_join(prepare_nhdplus(walker_flowline, 0, 0,
                            purge_non_dendritic = FALSE, warn = FALSE), by = "COMID") %>%
  select(ID = COMID, toID = toCOMID, length = LENGTHKM)

arb_sum <- calculate_arbolate_sum(catchment_length)

catchment_length$arb_sum <- arb_sum
catchment_length$nhd_arb_sum <- walker_flowline$ArbolateSu

mean(abs(catchment_length$arb_sum - catchment_length$nhd_arb_sum))
max(abs(catchment_length$arb_sum - catchment_length$nhd_arb_sum))