change behaviour of add. allow multiple values

R/data_rescale.R

@@ -15,12 +15,12 @@
 #'   For example, if a vector range from 5 to 15 and `multiply = 1.1`, the current
 #'   range of 10 will be expanded by the factor of 1.1, giving a new range of
 #'   11. Thus, the rescaled vector would range from 4.5 to 15.5.
-#' @param add If not `NULL`, `to` is ignored and `add` will be used, giving the
-#'   amount by which the actual range of `x` should be expanded. For example,
-#'   if a vector range from 5 to 15 and `add = 1`, the current range of 10 will
-#'   be expanded by 1, giving a new range of 11. Thus, the rescaled vector would
-#'   range from 4.5 to 15.5, because the lower and upper bounds are each expanded
-#'   by half of the amount specified in `add`.
+#' @param add A vector of length 1 or 2. If not `NULL`, `to` is ignored and `add`
+#'   will be used, giving the amount by which the minimum and maximum of the
+#'   actual range of `x` should be expanded. For example, if a vector range from
+#'   5 to 15 and `add = 1`, the range will be expanded from 4 to 16. If `add` is
+#'   of length 2, then the first value is used for the lower bound and the second
+#'   value for the upper bound.
 #' @param range Initial (old) range of values. If `NULL`, will take the range of
 #'   the input vector (`range(x)`).
 #' @param ... Arguments passed to or from other methods.
@@ -54,11 +54,10 @@
 #' x
 #' # both will expand the range by 10%
 #' rescale(x, multiply = 1.1)
-#' rescale(x, add = 1)
+#' rescale(x, add = 0.5)
 #'
-#' # "expand" range by 50%
-#' rescale(x, multiply = 1.5)
-#' rescale(x, add = 5)
+#' # expand range by different values
+#' rescale(x, add = c(1, 3))
 #'
 #' # Specify list of multipliers
 #' d <- data.frame(x = 5:15, y = 5:15)
@@ -317,11 +316,27 @@ rescale.data.frame <- function(x,
   }
   # multiply? If yes, calculate the "add" value
   if (!is.null(multiply)) {
-    add <- diff(range(x, na.rm = TRUE)) * (multiply - 1)
+    # check for correct length
+    if (length(multiply) > 1) {
+      insight::format_error("The length of `multiply` must be 1.")
+    }
+    add <- (diff(range(x, na.rm = TRUE)) * (multiply - 1)) / 2
   }
   # add?
   if (!is.null(add)) {
-    to <- c(min(x, na.rm = TRUE) - (add / 2), max(x, na.rm = TRUE) + (add / 2))
+    # add must be of length 1 or 2
+    if (length(add) > 2) {
+      insight::format_error("The length of `add` must be 1 or 2.")
+    }
+    # if add is of length 2, then the first value is used for the lower bound
+    # and the second value for the upper bound
+    if (length(add) == 2) {
+      add_low <- add[1]
+      add_high <- add[2]
+    } else {
+      add_low <- add_high <- add
+    }
+    to <- c(min(x, na.rm = TRUE) - add_low, max(x, na.rm = TRUE) + add_high)
   }
   to
 }

tests/testthat/test-data_rescale.R

@@ -120,8 +120,17 @@ test_that("data_rescale can expand range", {
     c(4.5, 5.6, 6.7, 7.8, 8.9, 10, 11.1, 12.2, 13.3, 14.4, 15.5),
     ignore_attr = TRUE
   )
-  expect_equal(rescale(x, multiply = 1.1), rescale(x, add = 1), ignore_attr = TRUE)
+  expect_equal(rescale(x, multiply = 1.1), rescale(x, add = 0.5), ignore_attr = TRUE)
   expect_error(rescale(x, multiply = 0.9, add = 1), regex = "Only one of")
+  expect_error(rescale(x, multiply = c(1.2, 1.4)), regex = "The length of")
+
+  # different values for add
+  expect_equal(
+    rescale(x, add = c(1, 3)),
+    c(4, 5.4, 6.8, 8.2, 9.6, 11, 12.4, 13.8, 15.2, 16.6, 18),
+    ignore_attr = TRUE
+  )
+  expect_error(rescale(x, add = 1:3), regex = "The length of")
 
   # works with NA
   expect_equal(
@@ -139,14 +148,28 @@ test_that("data_rescale can expand range", {
   d <- data.frame(x = 5:15, y = 5:15)
   expect_equal(
     rescale(d, multiply = 1.1),
-    rescale(d, add = 1),
+    rescale(d, add = 0.5),
     ignore_attr = TRUE
   )
   expect_equal(
     rescale(d, multiply = list(x = 1.1, y = 0.5)),
-    rescale(d, add = list(x = 1, y = -5)),
+    rescale(d, add = list(x = 0.5, y = -2.5)),
     ignore_attr = TRUE
   )
+  # data frames accept multiple add-values per column
+  out <- rescale(d, add = list(x = c(1, 3), y = c(2, 4)))
+  expect_equal(
+    out$x,
+    rescale(d$x, add = c(1, 3)),
+    ignore_attr = TRUE
+  )
+  expect_equal(
+    out$y,
+    rescale(d$y, add = c(2, 4)),
+    ignore_attr = TRUE
+  )
+
   expect_error(rescale(d, multiply = 0.9, add = 1), regex = "Only one of")
   expect_error(rescale(d, multiply = list(x = 0.9, y = 2), add = list(y = 1)), regex = "Only one of")
+  expect_error(rescale(d, multiply = c(0.9, 1.5)), regex = "The length of")
 })