td: Identity Function (Internal)

A simple identity function that returns the input as is. This function is typically used as a placeholder or for specific purposes like indicating time-dependent variables in model formulas.

td(x)

Arguments

x

A vector or object that is returned unchanged.

Value

The same value as the input.

Details

The `td` function does not modify the input value and simply returns it. It can be used in situations where a time-dependent covariate is needed in model formulas, typically in survival analysis models.