View source for IndexLength

[[Category:Functions returning information about arrays]]

''new to [[Analytica 5.0]]''

== IndexLength(I) ==

Returns the number of elements in Index «<code>I</code>».

[[IndexLength]] is closely related to the <code>[[Size]](a)</code> function, but differs in that <code>[[IndexLength]](I)</code> gives the size of the ''index'' <code>I</code>, whereas <code>[[Size]](a)</code> gives the size of the ''value'' <code>a</code>. For a simple, non-dynamic index, these are the same, but they are usually different in the case where <code>a</code> is a multi-dimensional [[Self-Indexed Arrays|self-indexed array]], or where the size of a dynamic index is requested from within a [[dynamic loop]].

<code>[[IndexLength]](I)</code> is equivalent to <code>[[Size]]([[IndexValue]](I))</code>, and to <code>[[Sum]](1,I)</code>.

== Examples ==

:<code>Index The_Date := Sequence( 20-Jan-2009, 19-Jan-2017) Do IndexLength(The_Date)</code> &rarr; 2922

Consider the case where variable <code>A</code> is a [[Self-Indexed Arrays|self-indexed array]]:
:Index Digit := <code>0..9</code>
:Variable A := [0,10,20,30] + Digit
:<code>[[Size]](A)</code> &rarr; 40
:<code>[[IndexLength]](A)</code> &rarr; 4

Suppose you need the length of the [[Time]] index from within a [[dynamic loop]]:
:Index Time := <code>2017..2025</code>
:<code>[[Dynamic]]( [[Size]](Time) )</code> &rarr; Array(Time, [1,1,1,1,1,1,1,1,1] )
:<code>[[Dynamic]]( [[IndexLength]](Time) )</code> &rarr; Array(Time, [9,9,9,9,9,9,9,9,9])
Inside a [[dynamic loop]], the ''value'' of [[Time] is the single time point, hence its [[Size]] is always 1. Hence, you should use [[IndexLength]] when you really want the length of the [[Time]] index.

== History ==

[[IndexLength]] was introduced as a built-in function in [[Analytica 5.0]]. Prior to [[Analytica 5.0]], you can define your own [[User-Defined Function]]:

:'''Function''' <code>IndexLength( I : Index ) := [[Size]](I)</code>

or use the more verbose expression <code>[[Size]]([[IndexValue]](I))</code> when you need the size of the index.

== See Also == 
* [[Size]]
* [[IndexValue]]