prev

    (PHP 4, PHP 5, PHP 7, PHP 8)

    prev — Rewind the internal array pointer

    Description

    prev(array|object &$array): mixed

    Rewind the internal array pointer.

    prev() behaves just like next(), except it rewinds the internal array pointer one place instead of advancing it.

    Parameters

    array

    The input array.

    Return Values

    Returns the array value in the previous place that's pointed to by the internal array pointer, or false if there are no more elements.

    Warning

    This function may return Boolean false, but may also return a non-Boolean value which evaluates to false. Please read the section on Booleans for more information. Use the === operator for testing the return value of this function.

    Changelog

    Version Description
    8.1.0 Calling this function on objects is deprecated. Either convert the object to an array using get_mangled_object_vars() first, or use the methods provided by a class that implements Iterator, such as ArrayIterator, instead.
    7.4.0 Instances of SPL classes are now treated like empty objects that have no properties instead of calling the Iterator method with the same name as this function.

    Examples

    Example #1 Example use of prev() and friends

    <?php
    $transport     = array('foot', 'bike', 'car', 'plane');
    $mode = current($transport); // $mode = 'foot';
    $mode = next($transport); // $mode = 'bike';
    $mode = next($transport); // $mode = 'car';
    $mode = prev($transport); // $mode = 'bike';
    $mode = end($transport); // $mode = 'plane';
    ?>

    Notes

    Note: The beginning of an array is indistinguishable from a bool false element. To make the distinction, check that the key() of the prev() element is not null.

    See Also

    • current() - Return the current element in an array
    • end() - Set the internal pointer of an array to its last element
    • next() - Advance the internal pointer of an array
    • reset() - Set the internal pointer of an array to its first element
    • each() - Return the current key and value pair from an array and advance the array cursor

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    User Contributed Notes 4 notes

    up
    0
    MicroVB INC
    10 years ago
    This function searches for the closest element in an array by key value, and returns the key/value pair, or false if not found.

    <?php
    function nearest($array, $value, $exact=false) {
    // Initialize Variables
    $next = false;
    $prev = false;
    $return = false;

    if(!isset(    $array[$value]) && !$exact) {
    // Insert element that doesn't exist so nearest can be found
    $array[$value] = '-';
    }

    if(    $exact && isset($array[$value])) {
    // If exact match found, and searching for exact (not nearest), return result.
    $return = Array($value=>$array[$value]);
    } else {
    // Sort array so injected record is near relative numerics
    ksort($array); // Sort array on key

    // Loop through array until match is found, then set $prev and $next to the respective keys if exist
    while ( !is_null($key = key($array)) ) {
    $val = current($array);
    if(    $key == $value) {
    prev($array); // Get entry before this one
    $prev = key($array);
    next($array); // Skip current entry as this was what we were looking for nearest to
    next($array); // Get entry after this one
    $next = key($array);
    break;
    }
    next($array);
    }

    if(    $prev && $next) {
    if((    $long - $prev) > ($next - $long)) {
    // Previous is closer
    $return = Array($prev=>$array[$prev]);
    } else {
    // Next is closer
    $return = Array($next=>$array[$next]);
    }
    } elseif (    $prev || $next) {
    if(    $prev) {
    // Only Previous exists
    $return = Array($prev=>$array[$prev]);
    } elseif (    $next) {
    // Only Next exists
    $return = Array($next=>$array[$next]);
    }
    }
    }

    // Return resulting Array(). $return is false if nothing matches the closest conditions, or if exact is specified and key does not exist.
    return $return;
    }
    ?>

    Example usage (to lookup the closest color in an array)
    <?php
    $mycolors    = Array(
    5001046=>'Abbey',
    1774596=>'Acadia',
    8171681=>'Acapulco',
    6970651=>'Acorn',
    13238245=>'Aero Blue',
    7423635=>'Affair',
    8803850=>'Afghan Tan',
    13943976=>'Akaroa',
    16777215=>'Alabaster',
    16116179=>'Albescent White',
    10176259=>'Alert Tan',
    30371=>'Allports'
    );

    // Color to search for in Hex
    $color = 'C0C0C0';

    // Convert Hex to Long to compare with array() keys
    $colorlong = base_convert($color,16,10);

    // Check for an exact match
    $result = nearest($mycolors, $colorlong, true);
    if(    $result) {
    echo     "An exact match was found for #" . $color . " which is called '" . $result[key($result)] . "'";
    } else {
    echo     "No exact match was found";
    }

    if(!    $result) {
    // Check for closest match
    $result = nearest($mycolors, $colorlong, true);
    if(    $result) {
    // Match found
    echo "The closest match for #" . $color . " is #" . base_convert(key($result),10,16) . " which is called '" . $result[key($result)] . "'";
    } else {
    // No match found
    echo "No match was found for #" . $color;
    }
    }
    ?>
    up
    -1
    soapergem at gmail dot com
    15 years ago
    Here's a slight revision to xmlich02's backwards iteration example. The problem with his/her example is that it will halt if any of the array elements are boolean false, while this version will not.

    <?php

    end    ($ar);
    while ( !    is_null($key = key($ar)) ) {
    $val = current($ar);
    echo     "{$key} => {$val}\n";
    prev($ar);
    }

    ?>
    up
    -2
    Mikhail
    4 years ago
    Function to get element in array, that goes previous your key or false if it not exeists or key doesn't isset in array.

    <?php

    function previousElement(array $array, $currentKey)
    {
    if (!isset(    $array[$currentKey])) {
    return     false;
    }
    end($array);
    do {
    $key = array_search(current($array), $array);
    $previousElement = prev($array);
    }
    while (    $key != $currentKey);

    return     $previousElement;
    }
    up
    -11
    MicroVB INC
    10 years ago
    Some corrections to the previous function.
    - When prev() and next() distance is now calculated properly returning the 'closer' one.
    - When exact is false, and an item exists with the key searched for, it now returns that entry instead of next/prev closest
    - At ends of the array, sometimes when moving past using next() or prev(), it caused results to die. This was corrected.
    - Added field to result stating whether the match was 'exact' ('exact'=>true), or nearest ('exact'=>false)

    <?php
    function nearest($array, $value, $exact=false) {
    // Initialize Variables
    $next = false;
    $prev = false;
    $return = false;

    $arr_begin = false;
    $arr_end = false;

    $exact_match = false;


    if(    $exact && isset($array[$value])) {
    // If exact match found, and searching for exact (not nearest), return result.
    $return = Array($value=>$array[$value]);
    $exact_match = true;
    } elseif (!    $exact && isset($array[$value])) {
    // If exact match found, and searching for nearest, return result.
    $return = Array($value=>$array[$value]);
    $exact_match = true;
    } else {

    if(!isset(    $array[$value]) && !$exact) {
    // Insert element that doesn't exist so nearest can be found
    $array[$value] = '-';
    }

    // Sort array so injected record is near relative numerics
    ksort($array); // Sort array on key

    // Set start and end keys
    $arr_begin = key($array);
    end($array);
    $arr_end = key($array);
    reset($array);

    // Loop through array until match is found, then set $prev and $next to the respective keys if exist
    while ( !is_null($key = key($array)) ) {
    $val = current($array);
    if(    $key == $value) {
    if(    $value <> $arr_begin) {
    prev($array); // Get entry before this one
    $prev = key($array);
    }

    next($array); // Skip current entry as this was what we were looking for nearest to

    if($value <> $arr_end) {
    next($array); // Get entry after this one
    $next = key($array);
    }
    break;
    }
    next($array);
    }

    if(    $prev && $next) {
    if((    $value - $prev) < ($next - $value)) {
    // Previous is closer
    $return = Array($prev=>$array[$prev]);
    } else {
    // Next is closer
    $return = Array($next=>$array[$next]);
    }
    } elseif (    $prev || $next) {
    if(    $prev) {
    // Only Previous exists
    $return = Array($prev=>$array[$prev]);
    } elseif (    $next) {
    // Only Next exists
    $return = Array($next=>$array[$next]);
    }
    }
    }

    // Return resulting Array(). $return is false if nothing matches the closest conditions, or if exact is specified and key does not exist.
    if($return) {
    return     $return+Array('exact'=>$exact_match);
    } else {
    return     false;
    }
    }
    ?>

    Just to clarify, this function will return either an Array() containing the $key=>$value pair of the result and 'exact'=>(bool) whether the match was exact or not.

    To access the $key=>$value pair, can be done as follows :
    <?php

    $result     = nearest( ... ); // Just here for clarification of the position for the code that follows.

    if($result) {
    // Output the Key
    echo key($result);

    // Output the Value
    echo $result( key($result) );

    // Output if exact match
    if($result['exact']) {
    echo     'This was an EXACT match';
    } else {
    echo     'This result was found with fuzzy logic';
    }

    } else {

    echo     'No result found';

    }

    ?>
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