Fix NA handling and creation #178
Description
> str(c(tf_rgp(3), NA))
tfd_reg [1:4]
$ 1: num [1:51] 1.099 1.049 1.034 0.957 0.952 ...
$ 2: num [1:51] -0.862 -0.695 -0.598 -0.503 -0.446 ...
$ 3: num [1:51] 0.277 0.243 0.224 0.18 0.129 ...
$ : NULL
> str(tf_rgp(3) - NA_real_)
tfd_reg [1:3]
$ 1: num [1:51] NA NA NA NA NA NA NA NA NA NA ...
$ 2: num [1:51] NA NA NA NA NA NA NA NA NA NA ...
$ 3: num [1:51] NA NA NA NA NA NA NA NA NA NA ...
still inconsistent NA handling / NA creation.
latter also breaks spark_rep_tf:
> tf_rgp(3) - NA_real_
tfd[3]: [0,1] -> [Inf,-Inf] based on 51 evaluations each
interpolation by tf_approx_linear
Error in `map()`:
ℹ In index: 1.
ℹ With name: 1.
Caused by error in `approx()`:
! need at least two non-NA values to interpolate