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Remove misleading example of NA in Levels section

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The levels section was using a level "NA" together with "female" and "male", which is misleading (given that NA was just introduced as a missing value). I updated it to what I believe is a better example of how NAs are interpreted.

Additionally, I edited a comment about Inf that wouldn't compile. How about inserting it at the tutorial altogether?
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Bruno Kim Medeiros Cesar 2014-11-01 01:37:26 -02:00
parent cd7a2e72d5
commit a32bb0a2cc
1 changed files with 6 additions and 5 deletions
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@ -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
@ -236,11 +236,12 @@ 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