/usr/share/doc/axiom-doc/hypertex/lin2darrays.xhtml

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 <body>
  <div align="center"><img align="middle" src="doctitle.png"/></div>
  <hr/>
  <div align="center">Two Dimensional Array</div>
  <hr/>
The <a href="db.xhtml?TwoDimensionalArray">TwoDimensionalArray</a> is used
for storing data in a two-dimensional data structure indexed by row and by
column. Such an array is a homogeneous data structure in that all the
entries of the array must belog to the same Axiom domain (although see
the <a href="axbook/section-2.6.xhtml">Any</a> domain). Each array has a
fixed number of rows and columns specified by the user and arrays are not
extensible. In Axiom, the indexing of two-dimensional arrays is one-based.
This means that both the "first" row of an array and the "first" column of
an array are given the index 1. Thus, the entry in the upper left corner
of an array is in position (1,1).

The operation <a href="dbopnew.xhtml">new</a> creates an array with a
specified number of rows and columns and fills the components of that
array with a specified entry. The arguments of this operation specify the
number of rows, the number of columns, and the entry. This creates a
five-by-four array of integers, all of which are zero.
<ul>
 <li>
  <input type="submit" id="p1" class="subbut" 
    onclick="makeRequest('p1');"
    value="arr:ARRAY2 INT:=new(5,4,0)" />
  <div id="ansp1"><div></div></div>
 </li>
</ul>
The entries of this array can be set to other integers using the
operation <a href="dbopsetelt.xhtml">setelt</a>.

Issue this to set the element in the upper left corner of this array to 17.
<ul>
 <li>
  <input type="submit" id="p2" class="subbut" 
    onclick="handleFree(['p1','p2']);"
    value="setelt(arr,1,1,17)" />
  <div id="ansp2"><div></div></div>
 </li>
</ul>
Now the first element of the array is 17.
<ul>
 <li>
  <input type="submit" id="p3" class="subbut" 
    onclick="handleFree(['p1','p2','p3']);"
    value="arr" />
  <div id="ansp3"><div></div></div>
 </li>
</ul>
Likewise, elements of an array are extracted using the operation
<a href="dbopelt.xhtml">elt</a>.
<ul>
 <li>
  <input type="submit" id="p4" class="subbut" 
    onclick="handleFree(['p1','p2','p4']);"
    value="elt(arr,1,1)" />
  <div id="ansp4"><div></div></div>
 </li>
</ul>
Another way to use these two operations is as follows. This sets the
element in position (3,2) of the array to 15.
<ul>
 <li>
  <input type="submit" id="p5" class="subbut" 
    onclick="handleFree(['p1','p2','p5']);"
    value="arr(3,2):=15" />
  <div id="ansp5"><div></div></div>
 </li>
</ul>
This extracts the element in position (,32) of the array.
<ul>
 <li>
  <input type="submit" id="p6" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p6']);"
    value="arr(3,2)" />
  <div id="ansp6"><div></div></div>
 </li>
</ul>
The operations <a href="dbopelt.xhtml">elt</a> and 
<a href="dbopsetelt.xhtml">setelt</a> come equipped with an error check which 
verifies that the indices are in the proper ranges. For example, the
above array has five rows and four columns, so if you ask for the entry
in position (6,2) with arr(6,2) Axiom displays an error message. If there
is no need for an error check, you can call the operations
<a href="dbopqelt.xhtml">qelt</a> and 
<a href="dbopqseteltbang.xhtml">qsetelt!</a> which provide the same 
functionality but without the error check. Typically, these operations
are called in well-tested programs.

The operations <a href="dboprow.xhtml">row</a> and
<a href="dbopcolumn.xhtml">column</a> extract rows and columns, 
respectively, and return objects of 
<a href="db.xhtml?OneDimensionalArray">OneDimensionalArray</a> with the
same underlying element type.
<ul>
 <li>
  <input type="submit" id="p7" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p7']);"
    value="row(arr,1)" />
  <div id="ansp7"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p8" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p8']);"
    value="column(arr,1)" />
  <div id="ansp8"><div></div></div>
 </li>
</ul>

You can determine the dimensions of an array by calling the operations
<a href="dbopnrows.xhtml">nrows</a> and <a href="dbopncols.xhtml">ncols</a>, 
which return the number of rows and columns, respectively.
<ul>
 <li>
  <input type="submit" id="p9" class="subbut" 
    onclick="handleFree(['p1','p9']);"
    value="nrows(arr)" />
  <div id="ansp9"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p10" class="subbut" 
    onclick="handleFree(['p1','p10']);"
    value="ncols(arr)" />
  <div id="ansp10"><div></div></div>
 </li>
</ul>
To apply an operation to every element of an array, use 
<a href="dbopmap.xhtml">map</a>. This creates a new array. This
expression negates every element.
<ul>
 <li>
  <input type="submit" id="p11" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p11']);"
    value="map(-,arr)" />
  <div id="ansp11"><div></div></div>
 </li>
</ul>
This creates an array where all the elements are doubled.
<ul>
 <li>
  <input type="submit" id="p12" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p12']);"
    value="map((x+->x+x),arr)" />
  <div id="ansp12"><div></div></div>
 </li>
</ul>
To change the array destructively, use 
<a href="dbopmapbang.xhtml">map!</a> instead of
<a href="dbopmap.xhtml">map</a>. If you need to make a copy of any array, 
use <a href="dbopcopy.xhtml">copy</a>.
<ul>
 <li>
  <input type="submit" id="p13" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p13']);"
    value="arrc:=copy(arr)" />
  <div id="ansp13"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p14" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p13','p14']);"
    value="map!(-,arrc)" />
  <div id="ansp14"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p15" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p13','p14','p15']);"
    value="arrc" />
  <div id="ansp15"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p16" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p16']);"
    value="arrc:=copy(arr)" />
  <div id="ansp16"><div></div></div>
 </li>
</ul>
Use <a href="dbopmemberq.xhtml">member?</a> to see if a given element 
is in an array.
<ul>
 <li>
  <input type="submit" id="p17" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p17']);"
    value="member?(17,arr)" />
  <div id="ansp17"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p18" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p18']);"
    value="member?(10317,arr)" />
  <div id="ansp18"><div></div></div>
 </li>
</ul>
To see how many times an element appears in an array, use 
<a href="dbopcount.xhtml">count</a>.
<ul>
 <li>
  <input type="submit" id="p19" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p19']);"
    value="count(17,arr)" />
  <div id="ansp19"><div></div></div>
 </li>
 <li>
  <input type="submit" id="p20" class="subbut" 
    onclick="handleFree(['p1','p2','p5','p20']);"
    value="count(0,arr)" />
  <div id="ansp20"><div></div></div>
 </li>
</ul>

For more information about the operations available for
<a href="db.xhtml?TwoDimensionalArray">TwoDimensionalArray</a>, issue
<ul>
 <li>
  <input type="submit" id="p21" class="subbut" 
    onclick="makeRequest('p21');"
    value=")show TwoDimensionalArray" />
  <div id="ansp21"><div></div></div>
 </li>
</ul>
For more information on related topics, see
<a href="pagematrix.xhtml">Matrix</a> and
<a href="lin1darrays.xhtml">OneDimensionalArray</a>
 </body>
</html>
axiom-hypertex-data 20120501-8 / usr / share / doc / axiom-doc / hypertex / lin2darrays.xhtml
