# IndexLength

*new to Analytica 5.0*

## IndexLength(I)

Returns the number of elements in index «I».

IndexLength is closely related to the Size function, but differs in that `IndexLength(I)`

gives the size of the *index* `I`

, whereas `Size(a)`

gives the size of the *value* `a`

. For a simple, non-dynamic index, these are the same, but they are usually different in the case where `a`

is a multi-dimensional self-indexed array, or where the size of a dynamic index is requested from within a dynamic loop.

`IndexLength(I)`

is equivalent to `Size(IndexValue(I))`

, and to `Sum(1, I)`

.

## Explanatory Video

**Video:** Why the IndexLength function is probably better than alternatives (4 minutes)

## Examples

`Index The_Date := Sequence(20-Jan-2009, 19-Jan-2017) Do IndexLength(The_Date) → 2922`

Consider the case where variable `A`

is a self-indexed array:

Index Digit := 0..9 Variable A := [0, 10, 20, 30] + Digit Size(A) → 40 IndexLength(A) → 4

Suppose you need the length of the Time index from within a dynamic loop:

Index Time := 2017..2025 Dynamic(Size(Time)) → Array(Time, [1, 1, 1, 1, 1, 1, 1, 1, 1]) Dynamic(IndexLength(Time)) → 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 by:

`Function IndexLength(I : Index) := Size(I)`

or use the more verbose expression `Size(IndexValue(I))`

when you need the size of the index.

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