CSC121 - R Console
Monday January 8th, 2018
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> # Simplest command is..nothing! The empty command. R does nothing and shows no output.
> 
> 
> # R as a calculator
> 2
[1] 2
> # Don't worry about the [1] for now, we'll talk about it later
> 2 + 3
[1] 5
> 11 + 56
[1] 67
> 12 - 2
[1] 10
> 4 * 5
[1] 20
> 2 + 3 + 5
[1] 10
> 2 ^ 3
[1] 8
> 2 ** 3
[1] 8
> # Anything after this # sign, is not evaluated
> # this is a comment
> # ** is the exponentiation operator 
>
> # Whitespace: R doesn't care how much whitespace you use, but use good style!
> 2 +                                                               3
[1] 5
> 1+2
[1] 3
> 2                 *                      7
[1] 14
> # GOOD STYLE: One space between operators and operands
> 4 + 5
[1] 9
> 8 / 3
[1] 2.666667
> 4 / 2
[1] 2
> # Can use 'typeof' to find type of the data
> typeof(2.4)
[1] "double"
> typeof(2)
[1] "double"
> # 'double' has nothing to do with the number 2.  typeof(3) is also double.
> 
> # as.integer returns the closest integer lower than the current number
> as.integer(2.4)
[1] 2
> as.integer(2.99999)
[1] 2
> as.integer(2.99999999999)
[1] 2
> # Case when too many trailing 9's can evaluate to higher integer
> as.integer(2.99999999999999999999999999)
[1] 3
> 
> as.integer(2.3426)
[1] 2
> typeof(as.integer(2.3426))
[1] "integer"
> as.double(2.43467)
[1] 2.43467
> 8 %% 3
[1] 2
> # %% is the modulor operator 
> # It gives back the remainder when dividing p / q
> 10 %% 2
[1] 0
> 11 %% 2
[1] 1
>
> # %/% Is integer division.  The result of p / q without the remainder.
>
> 4 %/% 2
[1] 2
> 8 %/% 3
[1] 2
> 8 / 3
[1] 2.666667
> 7 %/% 2
>
> # Negation
[1] 3
> -2
[1] -2
> --2
[1] 2
> # Can put lots of negative signs
> ------------------------------------------------------2
[1] 2
> 10 - -3
[1] 13
> # 10 "-" -3, this is the subtraction operator
> # 10 - "-"3, this is the negation operator
>
> # a [OPERATOR] b - we call this a binary operator
> # [OPERATOR]a - we call this a unary operator
> 
> # Compound Expressions:
> 10 + 2 * 3 + 4
[1] 20
> 10 * 2 + 3 * 4
[1] 32
> 10 * (2 + 3) * 4
[1] 200
> 
> # Precedence of operations
> # From high to low
> # ^ exponentiation 
> # - negation
> # *, /, %/%, %% - muliplication, division, modulo
> # +,- - addition, subtraction
> 
> # We want to store all of these expressions somewhere
> # VARIABLES
> p
Error: object 'p' not found
> # Need to 'define' p
> p <- 5
> p
[1] 5
> # To assign a value to a variable
> # variableName <- expression
> 
> p <- 2 ** 3 + 10
> p
[1] 18
> q <- p + 10
> q
[1] 28
> x <- 10
> x
[1] 10
> x <- x + 1
> x
[1] 11
> # We first evaluate the expression on the right side
> # and then we assign it to the variable on the left side
> y <- f + 2
Error: object 'f' not found
> # Need to define f before use it in an expression
> 
> x = 3
> # In R, we use the arrow <- to assign variables
> # Using '=' or others will make you lose marks for style
> q + 10 <- p
Error in q + 10 <- p : could not find function "+<-"
> # The left side must ONLY have a variable name -- the variable name you want 
> # to assign the expression on the right side to.
>
> # Errors:
> 2 + 4)*3
Error: unexpected ')' in "2 + 4)"
> 2 / 0 
[1] Inf
> # Infinity is a special number - we'll talk about it later
> 
> # VARIABLE Naming
> # A variable name can be any sequence of letters, digits, some symbols
> # It CAN'T start with "_", a digit, or with a '.' followed by a digit
> # choosing variable names is something you should learn to do well
> 
> # Camel case
> myAverage <- (1 + 2 + 10)/3
> # first letter lowercase, all other words uppercase
> 
> # Don't choose single letter words for variables in general
> # like q or p
> # Have a descriptive name that helps people understand what you are talking about
> 
> # doesn't work:
> 1lab <- 2
Error: unexpected symbol in "1lab"
> lab1 <- 2
> # works!
>