step_smote breaks with some over_ratios
rowanjh opened this issue · comments
The problem
step_smote throws an error when a class is marginally below the target upsampling threshold. This only occurs in rare cases when smote tries to synthesize a fraction of a sample (n < 1).
The issue occurs in themis:::smote_impl. When samples_needed contains a number smaller than 1, themis:::smote_data returns an empty matrix, subsequently causing an error at the line out_df[var] <- data[[names(samples_needed)[i]]][[var]][1]
One quick solution might be to floor the ratio_target when checking which classes need to be upsampled in themis:::smote_impl, as below. This would ignore the variables fractionally below the target threshold.
which_upsample <- which(table(df[[var]]) < ratio_target) # orig
which_upsample <- which(table(df[[var]]) < floor(ratio_target)) # possible solution
Reproducible example
library(recipes)
library(themis)
set.seed(123)
dat <- data.frame(
outcome = c(rep("X", 101), rep("Z", 50)),
X1 = rnorm(151))
rec_49 <- recipe(outcome ~ ., data = head(dat)) |>
step_smote(outcome, over_ratio = 0.49, seed = 231)
rec_50 <- recipe(outcome ~ ., data = head(dat)) |>
step_smote(outcome, over_ratio = 0.5, seed = 231)
rec_51 <- recipe(outcome ~ ., data = head(dat)) |>
step_smote(outcome, over_ratio = 0.51, seed = 231)
prep(rec_49, dat) # works
prep(rec_51, dat) # works
prep(rec_50, dat) # does not work
#> Error in `step_smote()`:
#> Caused by error in `[<-.data.frame`:
#> ! replacement has 1 row, data has 0
#> Backtrace:
#> x
#> 1. +-recipes::prep(rec_50, dat)
#> 2. +-recipes:::prep.recipe(rec_50, dat)
#> 3. | +-recipes:::recipes_error_context(...)
#> 4. | | +-base::withCallingHandlers(...)
#> 5. | | \-base::force(expr)
#> 6. | +-recipes::bake(x$steps[[i]], new_data = training)
#> 7. | \-themis:::bake.step_smote(x$steps[[i]], new_data = training)
#> 8. | +-withr::with_seed(...)
#> 9. | | \-withr::with_preserve_seed(...)
#> 10. | \-themis:::smote_impl(...)
#> 11. | +-base::`[<-`(`*tmp*`, var, value = `<fct>`)
#> 12. | \-base::`[<-.data.frame`(`*tmp*`, var, value = `<fct>`)
#> 13. | \-base::stop(...)
#> 14. \-base::.handleSimpleError(...)
#> 15. \-recipes (local) h(simpleError(msg, call))
#> 16. \-recipes:::stop_recipes_step(call = call(step_name), parent = cnd)
#> 17. \-recipes:::stop_recipes(...)
#> 18. \-rlang::abort(...)Created on 2023-02-08 with reprex v2.0.2
Session info
sessioninfo::session_info()
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#> date 2023-02-08
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#> ------------------------------------------------------------------------------
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