And and Or (SelectionCriterion functions): Difference between revisions

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<span style="font-size:120%; color:black"><b>Create selection expression based on logical operat</b></span>
{{Template:SelectionCriterion:And and Or subtitle}}
[[Category:SelectionCriterion methods|OR and AND constructors]]
<!--DPL?? Category:SelectionCriterion methods|OR and AND constructors: Create selection expression based on logical operat-->
<!--DPL?? Category:System methods|OR and AND (SelectionCriterion constructors): Create selection expression based on logical operat-->
<p>
OR and AND are members of the [[SelectionCriterion class]].
</p>


These shared methods each create a new SelectionCriterion object
These [[Notation conventions for methods#Shared members|shared methods]] each create a new <var>SelectionCriterion</var> object
that is an expression used to select the items in a collection.
that is an expression used to select the items in a collection.
Each constructor uses a different logical operator
Each function uses a different logical operator
to form an expression that combines one or more SelectionCriterion objects.
to form an expression that combines one or more <var>SelectionCriterion</var> objects.


An OR criterion returns true for a collection item if any of the
An <var>Or</var> criterion returns true for a collection item if any of the
component SelectionCriterion expressions are true for the item;
component <var>SelectionCriterion</var> expressions are true for the item;
otherwise it returns false.
otherwise it returns false.
An AND criterion returns true if all of the
An <var>And</var> criterion returns true if all of the
component SelectionCriterion expressions are true for the item;
component <var>SelectionCriterion</var> expressions are true for the item;
otherwise it returns false.
otherwise it returns false.


The collection searching method ([[??]] refid=srchcol.)
The [[Collections#Searching a collection|collection searching method]]
that makes use of a selection criterion specifies:
that makes use of a <var>SelectionCriterion</var> specifies:
<ul>
<ul>
<li>Whether to return the first item or item number or all items that satisfy the
<li>Whether to return the first item or item number or all items that satisfy the
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<li>Where in the collection to begin searching.
<li>Where in the collection to begin searching.
</ul>
</ul>
===OR syntax (same for AND)===
==Syntax==
  %selc = [%(selectionCriterion for itemtype):]  -
{{Template:SelectionCriterion:And syntax}}
            OR(criterion1 [,&nbsp;criterion2] ... [,&nbsp;criterionN])
{{Template:SelectionCriterion:Or syntax}}
 
===Syntax terms===
===Syntax terms===
<dl>
<table class="syntaxTable">
<dt><i>%selc</i>
<tr><th>%selectionCriterion</th>
<dd>A SelectionCriterion object variable to contain the new object instance.
<td>A <var>SelectionCriterion</var> object variable to contain the new object instance. </td></tr>
<dt><i>%(selectionCriterion for itemtype)</i>
<tr><th nowrap="true"><var>[%(SelectionCriterion For </var>itemType<var>):]</var>
<dd>This optional specification of the class and collection item type
<td>This optional specification of the class in parentheses denotes a [[Notation conventions for methods#Constructors|virtual constructor]]. See [[#Usage notes|"Usage notes"]], below, for more information about invoking a <var>SelectionCriterion</var> virtual constructor. </td></tr>
in parentheses indicates
<tr><th>list</th>
that the method is shared and does not operate on a specific instance.
<td>A comma-separated list of one or more <var>SelectionCriterion</var> objects. </td></tr>
<dt><i>criterion</i>
<dd>A SelectionCriterion object.


</dl>
</table>
===Usage Notes===
 
==Usage notes==
<ul>
<ul>
<li>All OR and AND SelectionCriterion conditions
<li>As described in [[Object variables#Virtual Constructor methods|"Virtual Constructor methods"]], <var>And</var> and <var>Or</var> can be invoked with
no method object, with an explicit class specification, or with an object variable of the class,
even if that object is <var>Null</var>:
<p class="code">%selCrit = And(<i>list</i>)
 
%selCrit = %(SelectionCriterion for float):Or(<i>list</i>)
 
%selCrit = %selCrit:And(<i>list</i>)
</p>
'''Note:'''
As shown in the second of these above, if you explicitly specify the
class name, you must include the item datatype of the collection to be searched, just as on a <var>SelectionCriterion</var> object variable's [[SelectionCriterion class#Declaring a SelectionCriterion object variable|declaration]].
<li>All <var>Or</var> and <var>And</var> <var>SelectionCriterion</var> conditions
are short-circuiting conditions.
are short-circuiting conditions.
That is, if any of the conditions in
That is, if any of the conditions in
an OR return True, the subsequent conditions are not evaluated and the
an <var>Or</var> return True, the subsequent conditions are not evaluated and the
OR returns True.
<var>Or</var> returns True.
Similarly, if any of the conditions in an AND return
Similarly, if any of the conditions in an <var>And</var> return
False, the subsequent conditions are not evaluated, and the AND returns a
False, the subsequent conditions are not evaluated, and the <var>And</var> returns a
False.
False.


Therefore, it is wise to put the most likely conditions first
Therefore, it is wise to put the most likely conditions first
in an OR, and it is wise to put the least likely first in an AND.
in an <var>Or</var>, and it is wise to put the least likely first in an <var>And</var>.
For a mix
For a mix
of conditions where some are simply variable references and others require
of conditions where some are simply variable references and others require
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first, as these are probably much cheaper to evaluate.
first, as these are probably much cheaper to evaluate.
</ul>
</ul>
===Examples===
 
==Examples==
<ol>
<ol>
<li>The following criterion
<li>The following criterion
matches numbers less than 70 and greater than or equal to 95:
matches numbers less than 70 and greater than or equal to 95:
<pre>
<p class="code">%sel = OR(lt(this,70), ge(this,95))
    %sel = OR(lt(this,70), ge(this,95))
</p>
</pre>
<li>The following criterion matches numbers that are
<li>The following criterion matches numbers that are
less than or equal to 33 but not 30:
less than or equal to 33 but not 30:
<pre>
<p class="code">%sel = AND(le(this, 33), ne(this,30)))
    %sel = AND(le(this, 33), ne(this,30)))
</p>
</pre>
</ol>
</ol>
==See also==
{{Template:SelectionCriterion:And and Or footer}}
[[Category:SelectionCriterion methods]]

Latest revision as of 21:11, 30 November 2011

Create selection expression based on logical operator (SelectionCriterion class)


These shared methods each create a new SelectionCriterion object that is an expression used to select the items in a collection. Each function uses a different logical operator to form an expression that combines one or more SelectionCriterion objects.

An Or criterion returns true for a collection item if any of the component SelectionCriterion expressions are true for the item; otherwise it returns false. An And criterion returns true if all of the component SelectionCriterion expressions are true for the item; otherwise it returns false.

The collection searching method that makes use of a SelectionCriterion specifies:

  • Whether to return the first item or item number or all items that satisfy the selection criterion.
  • Where in the collection to begin searching.

Syntax

%selectionCriterion = [%(SelectionCriterion For itemType):]And( list)

%selectionCriterion = [%(SelectionCriterion For itemType):]Or( list)

Syntax terms

%selectionCriterion A SelectionCriterion object variable to contain the new object instance.
[%(SelectionCriterion For itemType):] This optional specification of the class in parentheses denotes a virtual constructor. See "Usage notes", below, for more information about invoking a SelectionCriterion virtual constructor.
list A comma-separated list of one or more SelectionCriterion objects.

Usage notes

  • As described in "Virtual Constructor methods", And and Or can be invoked with no method object, with an explicit class specification, or with an object variable of the class, even if that object is Null:

    %selCrit = And(list) %selCrit = %(SelectionCriterion for float):Or(list) %selCrit = %selCrit:And(list)

    Note: As shown in the second of these above, if you explicitly specify the class name, you must include the item datatype of the collection to be searched, just as on a SelectionCriterion object variable's declaration.

  • All Or and And SelectionCriterion conditions are short-circuiting conditions. That is, if any of the conditions in an Or return True, the subsequent conditions are not evaluated and the Or returns True. Similarly, if any of the conditions in an And return False, the subsequent conditions are not evaluated, and the And returns a False. Therefore, it is wise to put the most likely conditions first in an Or, and it is wise to put the least likely first in an And. For a mix of conditions where some are simply variable references and others require method evaluation, it probably is best to put the variable references first, as these are probably much cheaper to evaluate.

Examples

  1. The following criterion matches numbers less than 70 and greater than or equal to 95:

    %sel = OR(lt(this,70), ge(this,95))

  2. The following criterion matches numbers that are less than or equal to 33 but not 30:

    %sel = AND(le(this, 33), ne(this,30)))

See also

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