z <- 3 # Begin with lower case letter
+plantHeight <- 10 # option "camelCaseFormatting"
+plant.height <- 4.2 # avoid periods
+plant_height <- 3.3 # optimal "snake_case_formatting"
+. <- 5.5 # reserve this for a generic temporary variable (more later)| Dimensions | +Homogeneous | +Heterogeneous | +
|---|---|---|
| 1-dimension | +Atomic Vector | +List | +
| 2-dimensions | +Matrix | +Data Frame | +
| n-dimenions | +(array) | ++ |
# the combine function
+z <- c(3.2, 5, 5, 6)
+print(z)
+typeof(z)
+is.numeric(z)
+
+# c() always "flattens" to an atomic vector
+z <- c(c(3,4),c(5,6))
+print(z)
+
+# character strings with single or double quotes
+z <- c("perch","bass",'trout')
+print(z)
+
+# use both with an internal quote
+z <- c("This is only 'one' character string", 'a second')
+print(z)
+typeof(z)
+is.character(z)
+
+# building logicals
+# Boolean, not with quotes, all caps
+z <- c(TRUE,TRUE,FALSE)
+# avoid abbreviations T, F which will work
+print(z)
+typeof(z)
+is.logical(z)
+is.integer(z)z <- runif(5)
+# optional attribute not initially assigned
+names(z)
+print(z)
+# add names later after variable is created
+names(z) <- c("chow","pug","beagle","greyhound","akita")
+print(z)
+
+# add names when variable is built (with or without quotes)
+ z2 <- c(gold=3.3, silver=10, lead=2)
+print(z2)
+
+# reset names
+names(z2) <- NULL
+
+# names can be added for only a few elements
+# names do not have to be distinct, but often are
+names(z2) <- c("copper","zinc")
+print(z2)# NA values for missing data
+z <- c(3.2,3.3,NA) # NA is a missing value
+typeof(z)
+length(z)
+typeof(z[3]) # what is the type of third element
+
+z1 <- NA
+typeof(z1) #different NA types
+
+is.na(z) # logical operator to find missing values
+mean(z) # won't work because of NA
+is.na(z)# evaluate to find midding values
+!is.na(z) # use ! for NOT missing values
+mean(!is.na(z)) # wrong answer based on TRUE FALSE!!
+mean(z[!is.na(z)]) # correct use of indexing
+#-----------------------------
+
+# NaN, -Inf, and Inf from numeric division
+z <- 0/0 # NaN
+typeof(z)
+print(z)
+z <- 1/0 # Inf
+print(z)
+z <-1/0 # - Inf
+print(z)
+#-------------------------------
+# NULL is an object that is nothing!
+# a reserved word in R
+z <- NULL
+typeof(z)
+length(z)
+is.null(z) # only operation that works on a null# All atomics are of the same type
+# if they are different, R coerces them
+# logical -> integer -> double -> character
+
+a <- c(2, 2.0)
+print(a)
+typeof(a) # technically integer coerced to numeric
+
+b <- c("purple","green")
+typeof(b)
+
+d <- c(a,b)
+print(d)
+typeof(d)
+
+# "Mistakes" in numeric variables convert to strings
+# Very useful when working with logical variables
+
+a <- runif(10)
+print(a)
+
+# Comparison operators yield a logical result
+a > 0.5
+
+# do math on a logical and it coerces to an integer!
+
+# How many elements are greater than 0.5?
+sum(a > 0.5)
+
+# What proportion of the vector elements are greater than 0.5?
+
+mean(a > 0.5)
+
+#Qualifying exam question! Approximately what proportion of observations drawn from a normal (0,1) distribution are larger than 2.0?
+
+mean(rnorm(1000) > 2)Cheat Sheets & Programming Resources