_{Official ZPE/YASS documentation}Map data types

A map stores key-value pairs. It is comparable to an associative array in PHP or a dictionary in several other languages. Keys identify values and do not need to be sequential numbers.

Creating maps

$scores = [
  "Jamie" => 92,
  "Jack" => 84
]

$empty_map = [=>]
  

The fat arrow separates each key from its value. Use [=>] when an explicitly typed empty map is required.

Accessing values

print($scores["Jamie"])
$scores["Joseph"] = 88
  

Filtering, selecting and ordering

Map predicates and selectors receive the key followed by the value.

where(function predicate) ⇒ map

Returns the original pairs for which the predicate returns true.

select(function projection) ⇒ list

Projects each key-value pair into a value in a new list.

order_by(function key_selector) ⇒ ordered map

Returns the original pairs ordered by the selected value.

$passed = $scores->where($name, $score => $score >= 50)
$names = $passed->select($name, $score => $name)
$ranked = $passed->order_by($name, $score => $score)
  

select and order_by were made available in ZPE 1.14.9 (Spurriergate, September 2026).

Legacy behaviour

Before ZPE 1.9.9, map functions used the associative_array_ prefix. The shorter map_ names are the current names; older aliases remain relevant when reading historical code.

Before ZPE 1.5.3, associative arrays used braces rather than square brackets. This changed the source syntax without changing the underlying map concept.