Here's an example of how to find duplicates:
library(tidyverse)
# Fake data
dat = data.frame(first=c("A","A","B","B", "C", "D"),
last=c("x","y","z","z", "w","u"),
value=c(1,2,3,3,4,5))
# Find duplicates (based on same first and last name)
dat %>%
group_by(first, last) %>%
filter(n()>1)
first last value
1 B z 3
2 B z 3
# Remove duplicates (keep only first instance of duplicated first and last name combinations)
dat %>%
group_by(first, last) %>%
slice(1)
first last value
1 A x 1
2 A y 2
3 B z 3
4 C w 4
5 D u 5