x < y.
Like all other FExpr operators, the less-than operator is elementwise:
it produces a column where each element is the result of comparison
x[i] < y[i].
y are multi-column expressions, then they must have the
same number of columns, and the
< operator will be applied to each
corresponding pair of columns. If either
y are single-column
while the other is multi-column, then the single-column expression
will be repeated to the same number of columns as its opponent.
The less-than operator can be applied to columns of any type, and the
y are allowed to be different. In the latter
case the columns will be converted into a common stype before the
The arguments must be either
FExprs, or expressions that can be
An expression that evaluates
x < y. The produced column will