[x] We can filter using expressions as in data.table, e.g. iris_tb[Species == "setosa",]
[x] We can filter by feeding a data.frame object to .i, in which case a semi join will be done, as used to be the case with data.table, but NOT a right join as is now the case with data.table
[x] A 2 side formula can be used to slice "along" a variable of group of variables, iris_tb[1:2 ~ Species]
iris_tb[Species == "setosa",].i, in which case a semi join will be done, as used to be the case with data.table, but NOT a right join as is now the case with data.tableiris_tb[1:2 ~ Species]