#584

R/find_transformation.R

@@ -5,13 +5,13 @@
 #'   or exp-transforming, was applied to the response variable (dependent
 #'   variable) in a regression formula. Currently, following patterns are
 #'   detected: `log`, `log1p`, `log2`, `log10`, `exp`, `expm1`, `sqrt`,
-#'   `log(x+<number>)` and `log-log`.
+#'   `log(x+<number>)`, `log-log` and `power` (to 2nd power, like `I(x^2)`).
 #'
 #' @param x A regression model.
 #' @return A string, with the name of the function of the applied transformation.
 #'   Returns `"identity"` for no transformation, and e.g. `"log(x+3)"` when
 #'   a specific values was added to the response variables before
-#'   log-transforming.
+#'   log-transforming. For unknown transformations, returns `NULL`.
 #'
 #' @examples
 #' # identity, no transformation
@@ -91,5 +91,19 @@ find_transformation <- function(x) {
     }
   }
 
+
+  # (unknown) I-transformation
+
+  if (any(grepl("I\\((.*)\\)", rv))) {
+    transform_fun <- NULL
+  }
+
+
+  # power-transformation
+
+  if (any(grepl("I\\((.*)\\^\\s*2\\)", rv))) {
+    transform_fun <- "power"
+  }
+
   transform_fun
 }

R/get_transformation.R

@@ -16,7 +16,8 @@
 #' transform the response variable; `$inverse`, the inverse-function of
 #' `$transformation` (can be used for "back-transformation"). If no
 #' transformation was applied, both list-elements `$transformation` and
-#' `$inverse` just return `function(x) x`.
+#' `$inverse` just return `function(x) x`. If transformation is unknown,
+#' `NULL` is returned.
 #'
 #' @examples
 #' # identity, no transformation
@@ -38,6 +39,11 @@
 get_transformation <- function(x) {
   transform_fun <- find_transformation(x)
 
+  # unknown
+  if (is.null(transform_fun)) {
+    return(NULL)
+  }
+
   if (transform_fun == "identity") {
     out <- list(transformation = function(x) x, inverse = function(x) x)
   } else if (transform_fun == "log") {
@@ -52,6 +58,8 @@ get_transformation <- function(x) {
     out <- list(transformation = exp, inverse = log)
   } else if (transform_fun == "sqrt") {
     out <- list(transformation = sqrt, inverse = function(x) x^2)
+  } else if (transform_fun == "power") {
+    out <- 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") {