From b4ca258612a9cc296931ef4607768cfb182aa21c Mon Sep 17 00:00:00 2001
From: Daniel <mail@danielluedecke.de>
Date: Wed, 26 Jun 2024 15:12:08 +0200
Subject: [PATCH] ...

---
 DESCRIPTION                              |  2 +-
 NEWS.md                                  |  3 +++
 R/get_transformation.R                   | 18 ++++++++++++------
 tests/testthat/test-get_transformation.R | 11 +++++++++++
 4 files changed, 27 insertions(+), 7 deletions(-)
 create mode 100644 tests/testthat/test-get_transformation.R

diff --git a/DESCRIPTION b/DESCRIPTION
index 74079e905..9ae5c6845 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,7 +1,7 @@
 Type: Package
 Package: insight
 Title: Easy Access to Model Information for Various Model Objects
-Version: 0.20.1.8
+Version: 0.20.1.9
 Authors@R: 
     c(person(given = "Daniel",
              family = "Lüdecke",
diff --git a/NEWS.md b/NEWS.md
index 5c0aa02a8..12305c672 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -32,6 +32,9 @@
 * `find_terms()` and `find_transformation()` now better cope with inverse
   transformations of the response value, such as `1/y`.
 
+* `get_transformation()` now returns more transformations for power-transformed
+  response variables.
+
 ## Bug fixes
 
 * `null_model()` now correctly handles zero-inflated models from package
diff --git a/R/get_transformation.R b/R/get_transformation.R
index 4e7f6848b..21c9c84d6 100644
--- a/R/get_transformation.R
+++ b/R/get_transformation.R
@@ -63,12 +63,18 @@ get_transformation <- function(x, verbose = TRUE) {
   } else if (transform_fun == "inverse") {
     out <- list(transformation = function(x) 1 / x, inverse = function(x) x^-1)
   } else if (transform_fun == "power") {
-    ## TODO: detect power - can we turn this into a function?
-    # power <- .safe(gsub("\\(|\\)", "", gsub("(.*)(\\^|\\*\\*)\\s*(\\d+|[()])", "\\3", find_terms(x)[["response"]])))
-    # if (is.null(power)) {
-    #   power <- 2
-    # }
-    out <- list(transformation = function(x) x^2, inverse = sqrt)
+    ## TODO: detect power - can we turn this into a generic function?
+    trans_power <- .safe(gsub("\\(|\\)", "", gsub("(.*)(\\^|\\*\\*)\\s*(\\d+|[()])", "\\3", find_terms(x)[["response"]]))) # nolint
+    if (is.null(trans_power)) {
+      trans_power <- "2"
+    }
+    out <- switch(trans_power,
+      `0.5` = list(transformation = function(x) x^0.5, inverse = function(x) x^2),
+      `3` = list(transformation = function(x) x^3, inverse = function(x) x^(1 / 3)),
+      `4` = list(transformation = function(x) x^4, inverse = function(x) x^0.25),
+      `5` = list(transformation = function(x) x^5, inverse = function(x) x^0.2),
+      list(transformation = function(x) x^2, inverse = sqrt)
+    )
   } else if (transform_fun == "expm1") {
     out <- list(transformation = expm1, inverse = log1p)
   } else if (transform_fun == "log-log") {
diff --git a/tests/testthat/test-get_transformation.R b/tests/testthat/test-get_transformation.R
new file mode 100644
index 000000000..db95650bc
--- /dev/null
+++ b/tests/testthat/test-get_transformation.R
@@ -0,0 +1,11 @@
+test_that("get_transformation - detect powers", {
+  data(iris)
+  m <- lm(Sepal.Length^2 ~ Species, data = iris)
+  fun <- get_transformation(m)
+  expect_identical(fun$transformation(2), 4)
+  expect_identical(fun$inverse(4), 2)
+  m <- lm(I(Sepal.Length^3) ~ Species, data = iris)
+  fun <- get_transformation(m)
+  expect_identical(fun$transformation(2), 8)
+  expect_identical(fun$inverse(8), 2)
+})