Мы можем использовать unique
из base R
unique(df1)
# City Lat Long Mals
#1 Bog 1m2sS 05M34W 2000
#3 Bog 1m2sS 05M34W 3500
#4 Bog 6m3sS 10M34W 3400
данные
df1 <- structure(list(City = c("Bog", "Bog", "Bog", "Bog"), Lat = c("1m2sS",
"1m2sS", "1m2sS", "6m3sS"), Long = c("05M34W", "05M34W", "05M34W",
"10M34W"), Mals = c(2000L, 2000L, 3500L, 3400L)),
class = "data.frame", row.names = c(NA,
-4L))