Adding collections methods to the TabularReader interface

docs/9.0/reader/index.md

@@ -384,6 +384,114 @@ $records = $stmt->process($reader);
 //$records is a League\Csv\ResultSet object
 ```
 
+### Collection methods
+
+<p class="message-notice">New methods added in version <code>9.11</code>.</p>
+
+To ease working with the loaded CSV document the following methods derived from collection are added.
+Some are just wrapper methods around the `Statement` class while others use the iterable nature
+of the CSV document.
+
+#### Reader::each
+
+Iterates over the records in the CSV document and passes each item to a closure:
+
+```php
+use League\Csv\Reader;
+use League\Csv\Writer;
+
+$writer = Writer::createFromString('');
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$reader->each(function (array $record, int $offset) use ($writer) {
+     if ($offset < 10) {
+        return $writer->insertOne($record);
+     }
+
+     return false;
+});
+
+//$writer will contain at most 10 lines coming from the $reader document.
+// the iteration stopped when the closure return false.
+```
+
+#### Reader::exists
+
+Tests for the existence of an element that satisfies the given predicate.
+
+```php
+use League\Csv\Reader;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$exists = $reader->exists(fn (array $records) => in_array('twenty-five', $records, true));
+
+//$exists returns true if at cell one cell contains the word `twenty-five` otherwise returns false,
+```
+
+#### Reader::reduce
+
+Applies iteratively the given function to each element in the collection, so as to reduce the collection to
+a single value.
+
+```php
+use League\Csv\Reader;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$nbTotalCells = $reader->recude(fn (?int $carry, array $records) => ($carry ?? 0) + count($records));
+
+//$records contains the total number of celle contains in the CSV documents.
+```
+
+#### Reader::filter
+
+Returns all the elements of this collection for which your callback function returns `true`. The order and keys of the elements are preserved.
+
+<p class="message-info"> Wraps the functionality of <code>Statement::where</code>.</p>
+
+```php
+use League\Csv\Reader;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$records = $reader->filter(fn (array $record): => 5 === count($record));
+
+//$recors is a ResultSet object with only records with 5 elements
+```
+
+#### Reader::slice
+
+Extracts a slice of $length elements starting at position $offset from the Collection.
+If $length is `-1` it returns all elements from `$offset` to the end of the
+Collection. Keys have to be preserved by this method. Calling this
+method will only return the selected slice and NOT change the
+elements contained in the collection slice is called on.
+
+<p class="message-info"> Wraps the functionality of <code>Statement::offset</code>
+and <code>Statement::limit</code>.</p>
+
+```php
+use League\Csv\Reader;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$records = $reader->slice(10, 25);
+
+//$records contains up to 25 rows starting at the offest 10 (the eleventh rows)
+```
+
+#### Reader::sorted
+
+Sorts the CSV document while keeping the original keys.
+
+```php
+use League\Csv\Reader;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$records = $reader->sorted(fn (array $recordA, array $recordB) => $recordA['firstname'] <=> $recordB['firstname']);
+
+//$records is a ResultSet containing the sorted CSV document. 
+//The original $reader is not changed
+```
+
+<p class="message-info"> Wraps the functionality of <code>Statement::orderBy</code>.</p>
+
 ## Records conversion
 
 ### Json serialization

docs/9.0/reader/resultset.md

@@ -352,6 +352,127 @@ foreach ($records->fetchPairs() as $firstname => $lastname) {
 
 <p class="message-warning">If the <code>ResultSet</code> contains column names and the submitted arguments are not found, an <code>Exception</code> exception is thrown.</p>
 
+### Collection methods
+
+<p class="message-notice">New methods added in version <code>9.11</code>.</p>
+
+To ease working with the `ResultSet` the following methods derived from collection are added.
+Some are just wrapper methods around the `Statement` class while others use the iterable nature
+of the instance.
+
+#### ResultSet::each
+
+Iterates over the records in the CSV document and passes each item to a closure:
+
+```php
+use League\Csv\Reader;
+use League\Csv\Statement;
+use League\Csv\Writer;
+
+$writer = Writer::createFromString('');
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+
+$resultSet = Statement::create()->process($reader);
+$resultSet->each(function (array $record, int $offset) use ($writer) {
+     if ($offset < 10) {
+        return $writer->insertOne($record);
+     }
+
+     return false;
+});
+
+//$writer will contain at most 10 lines coming from the $resultSet.
+// the iteration stopped when the closure return false.
+```
+
+#### ResultSet::exists
+
+Tests for the existence of an element that satisfies the given predicate.
+
+```php
+use League\Csv\Reader;
+use League\Csv\Statement;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$resultSet = Statement::create()->process($reader);
+
+$exists = $resultSet->exists(fn (array $records) => in_array('twenty-five', $records, true));
+
+//$exists returns true if at cell one cell contains the word `twenty-five` otherwise returns false,
+```
+
+#### Reader::reduce
+
+Applies iteratively the given function to each element in the collection, so as to reduce the collection to
+a single value.
+
+```php
+use League\Csv\Reader;
+use League\Csv\Statement;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$resultSet = Statement::create()->process($reader);
+
+$nbTotalCells = $resultSet->recude(fn (?int $carry, array $records) => ($carry ?? 0) + count($records));
+
+//$records contains the total number of celle contains in the $resultSet
+```
+
+#### Reader::filter
+
+Returns all the elements of this collection for which your callback function returns `true`. The order and keys of the elements are preserved.
+
+<p class="message-info"> Wraps the functionality of <code>Statement::where</code>.</p>
+
+```php
+use League\Csv\Reader;
+use League\Csv\Statement;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$resultSet = Statement::create()->process($reader);
+
+$records = $resultSet->filter(fn (array $record): => 5 === count($record));
+
+//$recors is a ResultSet object with only records with 5 elements
+```
+
+#### Reader::slice
+
+Extracts a slice of $length elements starting at position $offset from the Collection. If $length is `-1` it returns all elements from `$offset` to the end of the Collection.
+Keys have to be preserved by this method. Calling this method will only return the selected slice and NOT change the elements contained in the collection slice is called on.
+
+<p class="message-info"> Wraps the functionality of <code>Statement::offset</code> and <code>Statement::limit</code>.</p>
+
+```php
+use League\Csv\Reader;
+use League\Csv\Statement;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$resultSet = Statement::create()->process($reader);
+
+$records = $resultSet->slice(10, 25);
+
+//$records contains up to 25 rows starting at the offset 10 (the eleventh rows)
+```
+
+#### Reader::sorted
+
+Sorts the CSV document while keeping the original keys.
+
+<p class="message-info"> Wraps the functionality of <code>Statement::orderBy</code>.</p>
+
+```php
+use League\Csv\Reader;
+
+$reader = Reader::createFromPath('/path/to/my/file.csv', 'r');
+$resultSet = Statement::create()->process($reader);
+
+$records = $resultSet->sorted(fn (array $recordA, array $recordB) => $recordA['firstname'] <=> $recordB['firstname']);
+
+//$records is a ResultSet containing the original resultSet. 
+//The original ResultSet is not changed
+```
+
 ## Conversions
 
 ### Json serialization

src/Reader.php

@@ -14,6 +14,7 @@
 namespace League\Csv;
 
 use CallbackFilterIterator;
+use Closure;
 use Iterator;
 use JsonSerializable;
 use SplFileObject;
@@ -232,6 +233,85 @@ public function jsonSerialize(): array
         return array_values([...$this->getRecords()]);
     }
 
+    /**
+     * @param Closure(array<string|null>, array-key=): (void|bool|null) $closure
+     */
+    public function each(Closure $closure): bool
+    {
+        foreach ($this as $offset => $record) {
+            if (false === $closure($record, $offset)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    /**
+     * @param Closure(array<string|null>, array-key=): bool $closure
+     */
+    public function exists(Closure $closure): bool
+    {
+        foreach ($this as $offset => $record) {
+            if (true === $closure($record, $offset)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * @param Closure(TInitial|null, array<string|null>, array-key=): TInitial $closure
+     * @param TInitial|null $initial
+     *
+     * @template TInitial
+     *
+     * @return TInitial|null
+     */
+    public function reduce(Closure $closure, mixed $initial = null): mixed
+    {
+        foreach ($this as $offset => $record) {
+            $initial = $closure($initial, $record, $offset);
+        }
+
+        return $initial;
+    }
+
+    /**
+     * @param Closure(array<string|int>, array-key): bool $closure
+     *
+     * @throws Exception
+     * @throws SyntaxError
+     */
+    public function filter(Closure $closure): TabularDataReader
+    {
+        return Statement::create()->where($closure)->process($this);
+    }
+
+    /**
+     * @param int<0, max> $offset
+     * @param int<-1, max> $length
+     *
+     * @throws Exception
+     * @throws SyntaxError
+     */
+    public function slice(int $offset, int $length = -1): TabularDataReader
+    {
+        return Statement::create()->offset($offset)->limit($length)->process($this);
+    }
+
+    /**
+     * @param Closure(array<string|null>, array<string|null>): int $orderBy
+     *
+     * @throws Exception
+     * @throws SyntaxError
+     */
+    public function sorted(Closure $orderBy): TabularDataReader
+    {
+        return Statement::create()->orderBy($orderBy)->process($this);
+    }
+
     /**
      * @param array<string> $header
      *