fix when overwriting existing variables in grouped_df (#434)

DESCRIPTION

@@ -1,7 +1,7 @@
 Type: Package
 Package: datawizard
 Title: Easy Data Wrangling and Statistical Transformations
-Version: 0.7.1.11
+Version: 0.7.1.12
 Authors@R: c(
     person("Indrajeet", "Patil", , "[email protected]", role = "aut",
            comment = c(ORCID = "0000-0003-1995-6531", Twitter = "@patilindrajeets")),

R/data_modify.R

@@ -240,7 +240,12 @@ data_modify.grouped_df <- function(data, ...) {
 
   # create new variables as dummys, do for-loop works
   for (i in names(dots)) {
-    data[[i]] <- NA
+    # don't overwrite / fill existing variables with NA,
+    # e.g. if we have "data_modify(iris, Sepal.Length = normalize(Sepal.Length))"
+    # normalize() won't work when we fill with NA
+    if (!i %in% colnames(data)) {
+      data[[i]] <- NA
+    }
   }
 
   # create new variables per group

tests/testthat/test-data_modify.R

@@ -467,3 +467,18 @@ test_that("data_modify works with character variables, and inside functions", {
     tolerance = 1e-3
   )
 })
+
+
+test_that("data_modify works with grouped df when overwriting existing variables", {
+  data(iris)
+  iris_grp <- data_group(iris, "Species")
+  out <- data_modify(iris_grp, Sepal.Length = normalize(Sepal.Length))
+  expect_equal(head(out$Sepal.Length), c(0.53333, 0.4, 0.26667, 0.2, 0.46667, 0.73333), tolerance = 1e-3)
+
+  out <- data_modify(
+    iris_grp,
+    Sepal.Length = normalize(Sepal.Length),
+    Sepal.Length2 = 2 * Sepal.Length
+  )
+  expect_equal(head(out$Sepal.Length2), 2 * c(0.53333, 0.4, 0.26667, 0.2, 0.46667, 0.73333), tolerance = 1e-3)
+})