Handle named vector in levels argument of grid_regular

[juliasilge]

Closes #105.

This PR changes how the levels argument handles names; if names exist and match the parameter names, they are matched up before we map across both with map2(). There are also two little tests and some updated docs.

The right number of levels now gets assigned to the right parameter, no matter what order they are in the named vector:

library(tidymodels)
#> ── Attaching packages ───────────────────────────────────────────────────────────────── tidymodels 0.1.0 ──
#> ✓ broom     0.5.6          ✓ recipes   0.1.12    
#> ✓ dials     0.0.6.9000     ✓ rsample   0.0.6     
#> ✓ dplyr     1.0.0          ✓ tibble    3.0.1     
#> ✓ ggplot2   3.3.0          ✓ tune      0.1.0     
#> ✓ infer     0.5.1          ✓ workflows 0.1.1     
#> ✓ parsnip   0.1.1          ✓ yardstick 0.0.6     
#> ✓ purrr     0.3.4
#> ── Conflicts ──────────────────────────────────────────────────────────────────── tidymodels_conflicts() ──
#> x purrr::discard()  masks scales::discard()
#> x dplyr::filter()   masks stats::filter()
#> x dplyr::lag()      masks stats::lag()
#> x ggplot2::margin() masks dials::margin()
#> x recipes::step()   masks stats::step()

rf_spec <- rand_forest(trees = tune(), mtry = tune(), min_n = tune()) %>%
  set_mode("classification") %>%
  set_engine("ranger")

rf_wf <- workflow() %>% 
  add_model(rf_spec)

rf_params <- parameters(rf_wf) %>%
  update(trees = trees(c(100L, 200L))) %>%
  update(mtry = mtry(c(1L, 5L))) %>%
  update(min_n = min_n(c(10L, 20L))) %>%
  finalize()

rf_params$name
#> [1] "mtry"  "trees" "min_n"

levels_vec1 <- c(trees = 3, mtry = 2, min_n = 4)
levels_vec2 <- c(mtry = 2, trees = 3, min_n = 4)
levels_vec3 <- c(min_n = 4, mtry = 2,  trees = 3)

grid_regular(rf_params, levels = levels_vec1)
#> # A tibble: 24 x 3
#>     mtry trees min_n
#>    <int> <int> <int>
#>  1     1   100    10
#>  2     5   100    10
#>  3     1   150    10
#>  4     5   150    10
#>  5     1   200    10
#>  6     5   200    10
#>  7     1   100    13
#>  8     5   100    13
#>  9     1   150    13
#> 10     5   150    13
#> # … with 14 more rows
grid_regular(rf_params, levels = levels_vec2)
#> # A tibble: 24 x 3
#>     mtry trees min_n
#>    <int> <int> <int>
#>  1     1   100    10
#>  2     5   100    10
#>  3     1   150    10
#>  4     5   150    10
#>  5     1   200    10
#>  6     5   200    10
#>  7     1   100    13
#>  8     5   100    13
#>  9     1   150    13
#> 10     5   150    13
#> # … with 14 more rows
grid_regular(rf_params, levels = levels_vec3)
#> # A tibble: 24 x 3
#>     mtry trees min_n
#>    <int> <int> <int>
#>  1     1   100    10
#>  2     5   100    10
#>  3     1   150    10
#>  4     5   150    10
#>  5     1   200    10
#>  6     5   200    10
#>  7     1   100    13
#>  8     5   100    13
#>  9     1   150    13
#> 10     5   150    13
#> # … with 14 more rows

^{Created on 2020-06-08 by the reprex package (v0.3.0.9001)}

[juliasilge]

This now causes an error:

library(dials)
#> Loading required package: scales
p <- parameters(penalty(), mixture(), neighbors())
grid_regular(p, levels = c(2, penalty = 5, 6))
#> Error: Elements of `levels` should either be all named or unnamed, not mixed.

^{Created on 2020-06-09 by the reprex package (v0.3.0.9001)}

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