group data by name

General
2

If I understand you correctly this is what you are trying to do, if not, then please provide a REPRoducible EXample (reprex) illustrating your issue

library(tidyverse)
# Sample data to illustrate the problem
df <- data.frame(stringsAsFactors = FALSE,
                 section  = c("ALICE_!AAAA", "!AAAA_!AAAB", "!AAAB_NADIR",
                              "NADIR_!AAAC", "!AAAC_MANDI")
)

df %>% 
    mutate(beginning = str_extract(section, "^[^!]+(?=_)"),
           end = str_extract(section, "(?<=_)[^!]+$")) %>% 
    fill(beginning, .direction = "down") %>% 
    fill(end, .direction = "up") %>% 
    transmute(line = paste(beginning, end, sep = "_"), section = section)
#>          line     section
#> 1 ALICE_NADIR ALICE_!AAAA
#> 2 ALICE_NADIR !AAAA_!AAAB
#> 3 ALICE_NADIR !AAAB_NADIR
#> 4 NADIR_MANDI NADIR_!AAAC
#> 5 NADIR_MANDI !AAAC_MANDI

Created on 2019-10-07 by the reprex package (v0.3.0.9000)