Common Patterns

Common Programming Patterns Using Sequence

Table of Content

• Basic Patterns
• Sorting

Basic

Extract a value

Making a list of ids from an array of records is quite common. Here are two approaches.

$employeeIds = Sequence::make($employees)   // make the array into a Sequence
    ->pluck('employeeId')                   // Extract the employee id
    ->to_a();                               // Convert it into an array

Behind the scenes, ->pluck('fieldName') is just an alias for:
->map(fn\fnPluck('fieldName'))

$employeeIds = Sequence::make($employees)   // make the array into a Sequence
    ->map(fn\fnPluck('employeeId'))         // Extract the employee id
    ->to_a();                               // Convert it into an array

Index an array by a field value

$employeeIds = Sequence::make($employees)   // make the array into a Sequence
    ->keyBy(fn\fnPluck('employeeId'))       // Extract the employee id as assign it to the key
    ->to_a();                               // Convert it into an array

Extract array keys

The easiest way to get the keys from an array or iterator:

$keys = Sequence::make($peopleKeyedById)    // make the array|iterator into a Sequence
    ->keys()                                // get the keys
    ->to_a();

Using a Closure function (Note: ->map passes the key in as the second parameter):

$keys = Sequence::make($peopleKeyedById)    // make the array|iterator into a Sequence
    ->map(function ($value, $key) {         // write a Closure to extract $key
        return $key;
    })
    ->values()                              // Re-key starting with 0
    ->to_a();

A more sophisticated way that shows some useful functions:

$keys = Sequence::make($peopleKeyedById)
    ->map(fn\fnSwapParamsPassThrough(fn\fnIdentity()))
    ->values()
    ->to_a();

fnSwapParamsPassThrough will swap the $value and $key param and call fnIdentity. fnIdentity returns the first parameter.

$fn = fn\fnIdentity();
$true = $fn(101) === 101;

Sorting

Sort by a field

$employeesSortedById = Sequence::make($employees)   // make the array into a Sequence
    ->sort(fn\fnCompareField('employeeId'))         // sort the employees by their id
    ->to_a();

Sort by a field reverse

$employeesSortedById = Sequence::make($employees)   // make the array into a Sequence
    ->sort(fn\fnCompareFieldRev('employeeId'))      // sort the employees by their id in reverse order
    ->to_a();

Sorting and Keys

The following example will first sort the list and then key by the employee id:

$employeesSortedById = Sequence::make($employees)   // make the array into a Sequence
    ->sort(fn\fnCompareField('lastName'))           // sort the employees by their last name
    ->keyBy(fn\fnPluck('employeeId'))               // key by the employee id
    ->to_a();

To sort and preserve the keys, use asort instead of sort:

$employeesSortedById = Sequence::make($employees)   // make the array into a Sequence
    ->keyBy(fn\fnPluck('employeeId'))               // key by the employee id
    ->asort(fn\fnCompareField('lastName'))          // sort the employees by their last name
    ->to_a();

Warning: sort does NOT preserve numeric keys, if you need to preserve the keys, use asort. The following will NOT be keyed by employeeId:

$employeesSortedById = Sequence::make($employees)   // make the array into a Sequence
    ->keyBy(fn\fnPluck('employeeId'))               // key by the employee id
    ->sort(fn\fnCompareField('lastName'))           // **Keys are lost**
    ->to_a();