1 files changed, 15 insertions, 6 deletions

diff --git a/r.html.markdown b/r.html.markdown
index b59fc29c..d3d725d3 100644
--- a/r.html.markdown
+++ b/r.html.markdown
@@ -8,7 +8,7 @@ filename: learnr.r
 
 R is a statistical computing language. It has lots of libraries for uploading and cleaning data sets, running statistical procedures, and making graphs. You can also run `R` commands within a LaTeX document.
 
-```python
+```r
 
 # Comments start with number symbols.
 
@@ -179,7 +179,7 @@ c(3,3,3,2,2,1) # 3 3 3 2 2 1
 # You can also have infinitely large or small numbers
 class(Inf)	# "numeric"
 class(-Inf)	# "numeric"
-# You might use "Inf", for example, in integrate( dnorm(x), 3, Inf);
+# You might use "Inf", for example, in integrate(dnorm, 3, Inf);
 # this obviates Z-score tables.
 
 # BASIC ARITHMETIC
@@ -229,6 +229,13 @@ FALSE != FALSE	# FALSE
 FALSE != TRUE	# TRUE
 # Missing data (NA) is logical, too
 class(NA)	# "logical"
+# Use | and & for logic operations.
+# OR
+TRUE | FALSE	# TRUE
+# AND
+TRUE & FALSE	# FALSE
+# You can test if x is TRUE
+isTRUE(TRUE)	# TRUE
 # Here we get a logical vector with many elements:
 c('Z', 'o', 'r', 'r', 'o') == "Zorro" # FALSE FALSE FALSE FALSE FALSE
 c('Z', 'o', 'r', 'r', 'o') == "Z" # TRUE FALSE FALSE FALSE FALSE
@@ -236,11 +243,12 @@ c('Z', 'o', 'r', 'r', 'o') == "Z" # TRUE FALSE FALSE FALSE FALSE
 # FACTORS
 # The factor class is for categorical data
 # Factors can be ordered (like childrens' grade levels) or unordered (like gender)
-factor(c("female", "female", "male", "NA", "female"))
-#  female female male   NA     female
-# Levels: female male NA
+factor(c("female", "female", "male", NA, "female"))
+#  female female male   <NA>   female
+# Levels: female male
 # The "levels" are the values the categorical data can take
-levels(factor(c("male", "male", "female", "NA", "female"))) # "female" "male"   "NA" 
+# Note that missing data does not enter the levels
+levels(factor(c("male", "male", "female", NA, "female"))) # "female" "male"
 # If a factor vector has length 1, its levels will have length 1, too
 length(factor("male")) # 1
 length(levels(factor("male"))) # 1
@@ -251,6 +259,7 @@ levels(infert$education) # "0-5yrs"  "6-11yrs" "12+ yrs"
 # NULL
 # "NULL" is a weird one; use it to "blank out" a vector
 class(NULL)	# NULL
+parakeet = c("beak", "feathers", "wings", "eyes")
 parakeet
 # =>
 # [1] "beak"     "feathers" "wings"    "eyes"