Merge pull request #4372 from mribeirodantas/patch-2

[r/en] Update content according to R 4.0.0

r.html.markdown

@@ -4,6 +4,7 @@ contributors:
     - ["e99n09", "http://github.com/e99n09"]
     - ["isomorphismes", "http://twitter.com/isomorphisms"]
     - ["kalinn", "http://github.com/kalinn"]
+    - ["mribeirodantas", "http://github.com/mribeirodantas"]
 filename: learnr.r
 ---
 
@@ -405,7 +406,7 @@ mat
 # [2,]    2    5
 # [3,]    3    6
 # Unlike a vector, the class of a matrix is "matrix", no matter what's in it
-class(mat) # => "matrix"
+class(mat) # => "matrix" "array"
 # Ask for the first row
 mat[1,]	# 1 4
 # Perform operation on the first column
@@ -478,9 +479,10 @@ class(students[,3])	# "factor"
 nrow(students)	# 6
 ncol(students)	# 3
 dim(students)	# 6 3
-# The data.frame() function converts character vectors to factor vectors
+# The data.frame() function used to convert character vectors to factor
-# by default; turn this off by setting stringsAsFactors = FALSE when
+# vectors by default; This has changed in R 4.0.0. If your R version is
-# you create the data.frame
+# older, turn this off by setting stringsAsFactors = FALSE when you
+# create the data.frame
 ?data.frame
 
 # There are many twisty ways to subset data frames, all subtly unalike