V-Fold Cross-Validation with Buffering

V-fold cross-validation (also known as k-fold cross-validation) randomly splits the data into V groups of roughly equal size (called "folds"). A resample of the analysis data consists of V-1 of the folds while the assessment set contains the final fold. These functions extend rsample::vfold_cv() and rsample::group_vfold_cv() to also apply an inclusion radius and exclusion buffer to the assessment set, ensuring that your analysis data is spatially separated from the assessment set. In basic V-fold cross-validation (i.e. no repeats), the number of resamples is equal to V.

Usage

spatial_buffer_vfold_cv(
  data,
  radius,
  buffer,
  v = 10,
  repeats = 1,
  strata = NULL,
  breaks = 4,
  pool = 0.1,
  ...
)

spatial_leave_location_out_cv(
  data,
  group,
  v = NULL,
  radius = NULL,
  buffer = NULL,
  ...,
  repeats = 1
)

Arguments

data

A data frame.

radius

Numeric: points within this distance of the initially-selected test points will be assigned to the assessment set. If NULL, no radius is applied.

buffer

Numeric: points within this distance of any point in the test set (after radius is applied) will be assigned to neither the analysis or assessment set. If NULL, no buffer is applied.

v

The number of partitions for the resampling. Set to NULL or Inf for the maximum sensible value (for leave-one-X-out cross-validation).

repeats

The number of times to repeat the V-fold partitioning.

strata

A variable in data (single character or name) used to conduct stratified sampling. When not NULL, each resample is created within the stratification variable. Numeric strata are binned into quartiles.

breaks

A single number giving the number of bins desired to stratify a numeric stratification variable.

pool

A proportion of data used to determine if a particular group is too small and should be pooled into another group. We do not recommend decreasing this argument below its default of 0.1 because of the dangers of stratifying groups that are too small.

...

These dots are for future extensions and must be empty.

group

A variable in data (single character or name) used to create folds. For leave-location-out CV, this should be a variable containing the locations to group observations by, for leave-time-out CV the time blocks to group by, and for leave-location-and-time-out the spatiotemporal blocks to group by.

Details

When radius and buffer are both NULL, spatial_buffer_vfold_cv is equivalent to rsample::vfold_cv() and spatial_leave_location_out_cv is equivalent to rsample::group_vfold_cv().

References

K. Le Rest, D. Pinaud, P. Monestiez, J. Chadoeuf, and C. Bretagnolle. 2014. "Spatial leave-one-out cross-validation for variable selection in the presence of spatial autocorrelation," Global Ecology and Biogeography 23, pp. 811-820, doi: 10.1111/geb.12161.

H. Meyer, C. Reudenbach, T. Hengl, M. Katurji, and T. Nauss. 2018. "Improving performance of spatio-temporal machine learning models using forward feature selection and target-oriented validation," Environmental Modelling & Software 101, pp. 1-9, doi: 10.1016/j.envsoft.2017.12.001.

Examples

data(Smithsonian, package = "modeldata")
Smithsonian_sf <- sf::st_as_sf(
  Smithsonian,
  coords = c("longitude", "latitude"),
  crs = 4326
)

spatial_buffer_vfold_cv(
  Smithsonian_sf,
  buffer = 500,
  radius = NULL
)
#> #  10-fold spatial cross-validation 
#> # A tibble: 10 × 2
#>    splits         id    
#>    <list>         <chr> 
#>  1 <split [11/2]> Fold01
#>  2 <split [17/2]> Fold02
#>  3 <split [11/2]> Fold03
#>  4 <split [11/2]> Fold04
#>  5 <split [11/2]> Fold05
#>  6 <split [11/2]> Fold06
#>  7 <split [17/2]> Fold07
#>  8 <split [17/2]> Fold08
#>  9 <split [11/2]> Fold09
#> 10 <split [13/2]> Fold10

data(ames, package = "modeldata")
ames_sf <- sf::st_as_sf(ames, coords = c("Longitude", "Latitude"), crs = 4326)
ames_neighborhoods <- spatial_leave_location_out_cv(ames_sf, Neighborhood)