Exploring S-Plus 5.1 on UNIX (SOL) - Part II

In the August 1999 issue of RSS matters we provided an introduction to using S-Plus on SOL (http://www.unt.edu/benchmarks/archives/1999/august99/rss.htm). In this issue we continue our exploration of S-Plus on SOL.

Constructing Expressions in S-Plus

To begin our session we must invoke S-Plus after logging onto SOL. Type "Splus5" at the UNIX prompt to start the S-Plus session. You should see the following screen:

S-Plus expressions are typed in at the ">" prompt. S-Plus will print out the results of the evaluation once the "Enter" key is pressed:

An incomplete expression will lead to a second prompt, "+". You can continue with your expression at the second prompt:

If the “+” prompt continues after pressing "Enter", then enter many “)” to get the “>” prompt back again. Then start your expression once again:

Scalars and Assignments

The assignment operator is the sequence of characters, "<" (less than) and "-" (hyphen). Assigning the variable “weight” the value of 190 we use the following:

Character values are inserted in quotes. If the quotes are omitted, S-Plus will look for a possibly non-existent data object called "Jim" to assign to the variable "person". The result is not printed until you enter the object name:

Vectors

The function "rnorm( )", returns a vector of random deviates from the normal distribution The "[n]" on the left shows where the row starts:

A single number is a vector of length 1. We can make vectors using the concatenation function, "c( )". Then we can assign the integers 1,2,3 to the vector x:

We can create a vector of names. Also we can create a vector of sequential integers using the function, "a:b", where a is the starting integer and b is the ending integer:

Object Names

Object names may contain letters, "abcDEF", or numbers, "0123456789", or a dot, ".". Examples of valid names: height, weight, x.var, .yvar, x.y.var, or x110. Objects names cannot use an underscore, a hyphen, begin with a number, or use reserved symbols. Examples of invalid object names: _xvar, y_var, x-yvar, 120xvar, T, F, or NA.

Handling Objects

We can list out all of the objects in our workspace:

Objects remain until removed, even if one quits S-Plus:

Objects as Variables

Objects can be used in expressions:

Vector Arithmetic

Scalar Functions work on an element-wise basis. It is also possible to perform scalar and vector arithmetic:

Logical Vectors

Expressions with relational operators return logical vectors, "T" is True, "F" is False:

Missing Values

A missing value is represented by "NA". Operations on NA return NA. The function is.na( ) checks for missing values:

Vector Indexing

S-Plus uses brackets, [ ], to select elements of a vector. Negative indices remove elements:

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Logical Indices

A logical index selects elements. Symbols for the logical operators are: "<" (less than), ">" (greater than), "<=" (less than or equal to), ">=" (greater than or equal to), " = =" (equal to), "!" (negation operator), "!=" (not equal to).

Replacement

You can use [ ] on the left hand side of an assignment, "<-" :

Next Time

Next time we will cover matrices, arrays, and lists, among other topics. Good luck with S-Plus!