Как указано в комментариях, это просто простое суммирование:
library(dplyr)
library(data.table)
#dplyr option
averageTable %>% mutate(`Standing Still` = sum(Head.up, Vigilance, Resting, Grooming),
Moving = sum(Fleeing, Moving),
Feeding = sum(Grazing, Browsing)) %>% select(Group.1, `Standing Still`, Moving, Grazing)
#Even better dplyr option thank @moody_mudskipper(I'm not a tidyverse aficionado)
averageTable %>% transmute(Group.1, `Standing Still` = sum(Head.up, Vigilance, Resting, Grooming),
Moving = sum(Fleeing, Moving),
Feeding = sum(Grazing, Browsing))
#data.table option
setDT(averageTable)
averageTable[, .(`Standing Still` = sum(Head.up, Vigilance, Resting, Grooming),
Moving = sum(Fleeing, Moving),
Feeding = sum(Grazing, Browsing)), by = "Group.1"]