We need to extract the 'V1' column and use it as row index in 'i' to subset the rows.
setDT(df)[df[,.I[.N>2],by=Name]$V1]
# Date Name Salary
#1: Q1 2015 ABC $10
#2: Q2 2015 ABC $11
#3: Q3 2015 ABC $15
Or a concise option with if and .SD
setDT(df)[, if(.N >2) .SD, by = Name]
# Name Date Salary
#1: ABC Q1 2015 $10
#2: ABC Q2 2015 $11
#3: ABC Q3 2015 $15
Just in case, if we need a dplyr method
library(dplyr)
df %>%
group_by(Name) %>%
filter(n() >2 )
# Date Name Salary
# <chr> <chr> <chr>
#1 Q1 2015 ABC $10
#2 Q2 2015 ABC $11
#3 Q3 2015 ABC $15
Or with base R, we can have a number of options, one with ave
df[with(df, ave(seq_along(Name), Name, FUN = length)>2),]
or using table
tbl <- table(df$Name)> 2
subset(df, Name %in% names(tbl)[tbl])
