I generated a data table
require(data.table)
DT <- data.table(
ID =c("b","b","b","a","a","c"),
a= 1:6,
b= 7:12,
c=13:18)
DT
The DT is shown in Environment. But print(DT) does not give an result in the console and class(DT) does not respond. View(DT) shows the generated table. Same is with a data table downloaded from the internet. I checked R-Studio and could not find any wrong settings.