Editing Array slicing (section)

===1998: [[S-Lang]]===
Array slicing was introduced in version 1.0. Earlier versions did not
support this feature.

Suppose that A is a 1-d array such as
<pre>
    A = [1:50];           % A = [1, 2, 3, ...49, 50]
</pre>
Then an array B of first 5 elements of A may be created using
<pre>
    B = A[[:4]];
</pre>
Similarly, B may be assigned to an array of the last 5 elements of A via:
<pre>
    B = A[[-5:]];
</pre>
Other examples of 1-d slicing include:
<pre>
    A[-1]                 % The last element of A
    A[*]                  % All elements of A
    A[[::2]]              % All even elements of A
    A[[1::2]]             % All odd elements of A
    A[[-1::-2]]           % All even elements in the reversed order
    A[[[0:3], [10:14]]]   % Elements 0-3 and 10-14
</pre>

Slicing of higher-dimensional arrays works similarly:
<pre>
    A[-1, *]              % The last row of A
    A[[1:5], [2:7]]       % 2d array using rows 1-5 and columns 2-7
    A[[5:1:-1], [2:7]]    % Same as above except the rows are reversed
</pre>

Array indices can also be arrays of integers. For example, suppose
that <code>I = [0:9]</code> is an array of 10 integers. Then
<code>A[I]</code> is equivalent to an array of the first 10 elements
of <code>A</code>. A practical example of this is a sorting
operation such as:
<pre>
    I = array_sort(A);    % Obtain a list of sort indices
    B = A[I];             % B is the sorted version of A
    C = A[array_sort(A)]; % Same as above but more concise.
</pre>