Running examples in 'origami-Ex.R' failed
The error most likely occurred in:

> ### Name: cross_validate
> ### Title: Main Cross-Validation Function
> ### Aliases: cross_validate
> 
> ### ** Examples
> 
> ###############################################################################
> # This example explains how to use the cross_validate function naively.
> ###############################################################################
> data(mtcars)
> 
> # resubstitution MSE
> r <- lm(mpg ~ ., data = mtcars)
> mean(resid(r)^2)
[1] 4.609201
> 
> # function to calculate cross-validated squared error
> cv_lm <- function(fold, data, reg_form) {
+   # get name and index of outcome variable from regression formula
+   out_var <- as.character(unlist(stringr::str_split(reg_form, " "))[1])
+   out_var_ind <- as.numeric(which(colnames(data) == out_var))
+ 
+   # split up data into training and validation sets
+   train_data <- training(data)
+   valid_data <- validation(data)
+ 
+   # fit linear model on training set and predict on validation set
+   mod <- lm(as.formula(reg_form), data = train_data)
+   preds <- predict(mod, newdata = valid_data)
+ 
+   # capture results to be returned as output
+   out <- list(coef = data.frame(t(coef(mod))),
+               SE = ((preds - valid_data[, out_var_ind])^2))
+   return(out)
+ }
> 
> # replicate the resubstitution estimate
> resub <- make_folds(mtcars, fold_fun = folds_resubstitution)[[1]]
> resub_results <- cv_lm(fold = resub, data = mtcars, reg_form = "mpg ~ .")
Error in namespaceExport(ns, exports) : 
  undefined exports: %s!=%, %s!==%, %s+%, %s<%, %s<=%, %s==%, %s===%, %s>%, %s>=%, %stri!=%, %stri!==%, %stri+%, %stri<%, %stri<=%, %stri==%, %stri===%, %stri>%, %stri>=%, stri_datetime_add<-, stri_sub<-, stri_subset<-, stri_subset_charclass<-, stri_subset_coll<-, stri_subset_fixed<-, stri_subset_regex<-, stri_c, stri_c_list, stri_cmp, stri_cmp_eq, stri_cmp_equiv, stri_cmp_ge, stri_cmp_gt, stri_cmp_le, stri_cmp_lt, stri_cmp_neq, stri_cmp_nequiv, stri_compare, stri_conv, stri_count, stri_count_boundaries, stri_count_charclass, stri_count_coll, stri_count_fixed, stri_count_regex, stri_count_words, stri_datetime_add, stri_datetime_create, stri_datetime_fields, stri_datetime_format, stri_datetime_fstr, stri_datetime_now, stri_datetime_parse, stri_datetime_symbols, stri_detect, stri_detect_charclass, stri_detect_coll, stri_detect_fixed, stri_detect_regex, stri_dup, stri_duplicated, stri_duplicated_any, stri_enc_detect, stri_enc_detect2, stri_enc_fromutf32, stri_enc_get, stri_enc_inf
Calls: cv_lm ... tryCatch -> tryCatchList -> tryCatchOne -> <Anonymous>
Execution halted