`<indexOf>`

The index of the first value in a list equal to each target, or 0 where there is noneAdded in 0.7.27

<indexOf> is a General Operator component that renders, for each value given by the target attribute, the position of the first of its arguments equal to that value. Indices start at 1, and a target that does not occur in the list gives 0. To find where a value belongs in a sorted list rather than whether it is there at all, use <searchSorted>.

Attributes and Properties

Attributes for `<indexOf>`

Highlighted (3)

asList

boolean. Default value: true. Whether to render the items separated by commas (true) or with no separator (false).

target

_componentListWithSelectableType. The value, or list of values, to look for.

type

keyword. Component type to interpret bare string children as. Omit it and they are read as what they look like: every piece naming a number makes the list numeric, anything else makes it text. Also decides how target is read, since it has no type of its own.

Value	Description
`number`	Read bare strings as numbers, ordered by value.
`math`	Read bare strings as math expressions, ordered by value.
`text`	Read bare strings as text, ordered alphabetically.
`boolean`	Read bare strings as booleans, ordered with false before true.

Number display (5)

avoidScientificNotation

boolean. Default value: false. Whether to render numbers in full decimal form rather than scientific notation.

displayDecimals

integer. Default value: 2. Number of decimal places to display when rendering this number.

displayDigits

integer. Default value: 3. Number of significant digits to display when rendering this number.

displaySmallAsZero

number. Default value: 1e-14. Threshold below which numbers are displayed as zero.

padZeros

boolean. Default value: false. Whether to pad displayed numbers with trailing zeros to fill the requested digits/decimals.

Common to all components (9)

copy

reference. Create an independent copy of another component by reference. Enter a references a $name.

disabled

boolean. Default value: false. Whether this component is disabled and cannot be interacted with.

extend

reference. Extend another component by reference, inheriting its children and attributes. Enter a reference as $name.

fixed

boolean. Default value: false. Whether this component's value is fixed and cannot be modified.

fixLocation

boolean. Default value: false. Whether this component's location is fixed (preventing it from being moved while still allowing other modifications).

hide

boolean. Default value: false. Whether to hide this component from the rendered output.

isResponse

boolean. Default value: false. Whether this component is treated as a response for the purposes of assessment.

name

text. The name used to reference this component from elsewhere in the document.

styleNumber

integer. Default value: 1. The style number used to select this component's visual styling from the available style definitions.

Properties for `<indexOf name="i">`

Number display (5)

$i.avoidScientificNotationIn development

boolean. Whether to render numbers in full decimal form rather than scientific notation.

$i.displayDecimalsIn development

integer. Number of decimal places to display when rendering this number.

$i.displayDigitsIn development

integer. Number of significant digits to display when rendering this number.

$i.displaySmallAsZeroIn development

number. Threshold below which numbers are displayed as zero.

$i.padZerosIn development

boolean. Whether to pad displayed numbers with trailing zeros to fill the requested digits/decimals.

Common to all components (8)

$i.disabledIn development

boolean. Whether this component is disabled and cannot be interacted with.

$i.doenetML

text. The DoenetML source code that produced this component.

$i.fixedIn development

boolean. Whether this component's value is fixed and cannot be modified.

$i.fixLocationIn development

boolean. Whether this component's location is fixed (preventing it from being moved while still allowing other modifications).

$i.hiddenIn development

boolean. Whether this component is hidden from the rendered output.

$i.hide

boolean. Whether to hide this component from the rendered output.

$i.isResponse

boolean. Whether this component is treated as a response for the purposes of assessment.

$i.styleNumber

integer. The style number used to select this component's visual styling from the available style definitions.

Examples

Example: finding a number

The value 20 occurs twice and the first occurrence is reported. A value that is absent gives 0, which is a position no list entry has.

Example: finding a name

type="text" tells <indexOf> to read the target as text rather than as a number.

Example: looking up several targets at once

There is one result per target, in the order the targets were given. Eve is not on the roster, so her slot is 0 while the others keep their positions.

Example: looking up a parallel list

Finding a position in one list and reading it out of another is the usual reason to want <indexOf> rather than a test for membership.

Example: indexing without naming the lookup

The <indexOf> can be written between the index brackets instead of being named and referenced. Both find the same position, so which to use is a matter of how the sentence reads: naming it keeps a long index out of the prose, and is what to do when the same position is wanted more than once.

A property can follow the brackets, as the second paragraph shows, and so can a further index.

Attribute Examples

Attribute Example: target

target is read the way bare children are: whitespace separates one target from the next, so target="New York" asks for two of them and neither is on the list. A value with a space in it is written as a <text> of its own and referenced — which is also how the list holding it is built, since <textList>Boston New York</textList> is three cities and not two.

<indexOf>