CSC121 - R Console
Friday January 12th
---------------------------
> # Last time we saw that as.integer(x) is a function
> as.integer(1 + 2 + 0.6)
[1] 3
> # Let's go through the evaluation stages
> # The function: as.integer(x)
> # Argument to the function in general: x
> # In our specific case of as.integer(1 + 2 + 0.6), the argument is: 1 + 2 + 0.6
> # ^ the argument is not '3.6' because we haven't evaluated it yet
> # Now, our function call steps:
> # Step 1: Evaluate the argument to the function
> #   1 + 2 + 0.6 = 3.6
> #   The value of the argument to the function is 3.6
> # Step 2: Call the function as.integer(x) with the value 3.6
> # After we called the function, we get a return value
> #   The return value of as.integer(3.6) = 3
> as.integer(1 + 2 + 0.6)
[1] 3
> 
> # Arguments that are functions themselves
> t <- sqrt(abs(-4))
> # Step 1: Evaluate the argument to the function sqrt
> #   The argument is abs(-4)       the argument is a function call!
> #   So we have to evaluate abs(-4)
> #       The argument to abs(-4) is -4
> #       After calling abs(-4) we get 4
> #   	  The return value of abs(-4) is 4
> #   We've evaluated the argument to sqrt(x), in this case it is 4
> # Step 2: Call the function with the value 4
> # The return value of sqrt(4) = 2
> t
[1] 2
> 
> # some other math functions:
> # Sinusoidal functions: sin(x) and cos(x)
> # Pi = 3.14159......  can't store infinite digits.  We'll talk later about how R handles these
> pi
[1] 3.141593
> sin(pi / 2)
[1] 1
> cos(pi)
[1] -1
> P <- abs(cos(pi))
> # what do we expect?
> # The argument to abs(x) is cos(pi)
> # the value of the argument is cos(pi) = -1
> # So now we have abs(-1)
> # So P should have the value 1
> P
[1] 1
> # You want to get faster at understanding how function calls and their arguments get evaluated
> # Practise!!!
> 
> # Important and USEFUL function!!!!!!!
> # help(x)
> # Put as an argument to help(x) a name of a function
> help(sqrt)
> # help(x) return on the right side of RStudio some help documentation for that function
> help(as.integer)
>
>