Collinearity not available for models of class 'hurdle'

Fixes #606

NEWS.md

@@ -9,6 +9,12 @@
 * `check_outliers()` for `"ICS"` method is now more stable and less likely to
   fail.
 
+## Bug fixes
+
+* `check_collinearity()` did not work for hurdle- or zero-inflated models of
+  package *pscl* when model had no explicitly defined formula for the
+  zero-inflation model.
+
 # performance 0.10.4
 
 ## Changes to functions

R/check_collinearity.R

@@ -440,6 +440,14 @@ check_collinearity.zerocount <- function(x,
 
   f <- insight::find_formula(x)
 
+  # hurdle or zeroinfl model can have no zero-inflation formula, in which case
+  # we have the same formula as for conditional formula part
+  if (inherits(x, c("hurdle", "zeroinfl", "zerocount")) &&
+      component == "zero_inflated" &&
+      is.null(f[["zero_inflated"]])) {
+    f$zero_inflated <- f$conditional
+  }
+
   if (inherits(x, "mixor")) {
     terms <- labels(x$terms)
   } else {

tests/testthat/test-check_collinearity.R

@@ -190,3 +190,24 @@ test_that("check_collinearity, ci are NA", {
     )
   )
 })
+
+test_that("check_collinearity, hurdle/zi models w/o zi-formula", {
+  skip_if_not_installed("pscl")
+  data("bioChemists", package = "pscl")
+  m <- pscl::hurdle(
+    art ~ fem + mar,
+    data = bioChemists,
+    dist = "poisson",
+    zero.dist = "binomial",
+    link = "logit"
+  )
+  out <- check_collinearity(m)
+  expect_identical(
+    colnames(out),
+    c(
+      "Term", "VIF", "VIF_CI_low", "VIF_CI_high", "SE_factor", "Tolerance",
+      "Tolerance_CI_low", "Tolerance_CI_high", "Component"
+    )
+  )
+  expect_equal(out$VIF, c(1.05772, 1.05772, 1.06587, 1.06587), tolerance = 1e-4)
+})