PHP: Hypertext Preprocessor

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

prev — Retrocede el puntero actual del array

Descripción

prev(array|object &$array): mixed

Retrocede el puntero actual del array.

prev() se comporta exactamente como next(), pero hace retroceder el puntero en lugar de avanzarlo.

Parámetros

array: El array de entrada.

Valores devueltos

Devuelve el valor anterior del array siguiendo el puntero interno del array, o false si no hay más elementos.

Advertencia

Esta función puede devolver el valor booleano false, pero también puede devolver un valor no booleano que se evalúa como false. Por favor lea la sección sobre Booleanos para más información. Use el operador === para comprobar el valor devuelto por esta función.

Historial de cambios

Versión	Descripción
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.

Ejemplos

Ejemplo #1 Ejemplo con prev()

<?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';
?>

Notas

Nota: No es posible distinguir el inicio de un array del elemento bool false. Para hacer la distinción, verifique si la key() del elemento prev() no es null.

Ver también

current() - Devuelve el elemento actual del array
end() - Posiciona el puntero del array al final del array
next() - Avance el puntero interno de un array
reset() - Reinicia el puntero interno del array al principio
each() - Devuelve cada par clave/valor de un array

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User Contributed Notes 3 notes

down

MicroVB INC ¶

11 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;
    }  
}
?>

down

-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);
}

?>

down

-2

Mikhail ¶

5 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;
}

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