Allow simulation from completely empty time grid

[kylebaron]

Summary

• Issue: rendering the time grid gives the value 0 when there are not times (add is numeric(0) and end is -1. That was originally done for safety, but it really isn't the behavior we want in certain cases
• See also Extra record in the output at time 0 when all evid==2 #476

SOLUTION:

• refactor render_time so that it is more efficient and can return numeric(0) if there are really no times
• We will still simulate a minimum time 0 record for each person by only if not doing so would result in zero rows in the output

Tests

• tests/testthat/test-tgrid.R
  • stime can render length 0
  • no extra time 0 record when no observations

[kylebaron]

library(mrgsolve)
#> 
#> Attaching package: 'mrgsolve'
#> The following object is masked from 'package:stats':
#> 
#>     filter

mod <- house(end = 24)

dose <- ev(amt = 0, ii = 1, addl = 4,evid=2) %>% realize_addl()

dose
#> Events:
#>   time amt ii addl cmt evid
#> 1    0   0  0    0   1    2
#> 2    1   0  0    0   1    2
#> 3    2   0  0    0   1    2
#> 4    3   0  0    0   1    2
#> 5    4   0  0    0   1    2

mod %>% mrgsim(ev = dose, end = -1)
#> Model:  housemodel 
#> Dim:    6 x 7 
#> Time:   0 to 4 
#> ID:     1 
#>     ID time GUT CENT RESP DV CP
#> 1:   1    0   0    0   50  0  0
#> 2:   1    0   0    0   50  0  0
#> 3:   1    1   0    0   50  0  0
#> 4:   1    2   0    0   50  0  0
#> 5:   1    3   0    0   50  0  0
#> 6:   1    4   0    0   50  0  0

^{Created on 2020-03-14 by the reprex package (v0.3.0)}

[kylebaron]

library(mrgsolve)
#> 
#> Attaching package: 'mrgsolve'
#> The following object is masked from 'package:stats':
#> 
#>     filter

mod <- house(end = 24)

dose <- ev(amt = 0, ii = 1, addl = 4,evid=2) %>% realize_addl()

dose
#> Events:
#>   time amt ii addl cmt evid
#> 1    0   0  0    0   1    2
#> 2    1   0  0    0   1    2
#> 3    2   0  0    0   1    2
#> 4    3   0  0    0   1    2
#> 5    4   0  0    0   1    2

mod %>% mrgsim(ev = dose, end = -1)
#> Model:  housemodel 
#> Dim:    5 x 7 
#> Time:   0 to 4 
#> ID:     1 
#>     ID time GUT CENT RESP DV CP
#> 1:   1    0   0    0   50  0  0
#> 2:   1    1   0    0   50  0  0
#> 3:   1    2   0    0   50  0  0
#> 4:   1    3   0    0   50  0  0
#> 5:   1    4   0    0   50  0  0

^{Created on 2020-03-14 by the reprex package (v0.3.0)}

[kylebaron]

Fixed tests in inst/maintenance/unit/test-nocb.R to be consistent with new behavior.