PHP is_sequence() concept to implement on Math library

concept.md

This is only a concept to be analyzed

is_sequence

is_sequence - Verify if number range have correct sequence or arithmetic progression

Description

bool is_sequence ( array $array , int|float $sequence [, int $flags ] )

Parameters

array

array with numbers to validation

sequence

sequence number to validation

flags

set if number sequence is positive or negative

Avaliable flags

Flag	Description
SEQUENCE_POSITIVE	Define sequence as positive
SEQUENCE_NEGATIVE	Define sequence as negative

Return Values

This function return TRUE if array sequence is correct, FALSE otherwise.

Examples

Example #1 is_sequence() examples

<?php
$array = array(5, 7, 9, 11, 13);
$sequence = 2;

if (is_sequence($array, $sequence) === true) {
    echo "Yes, ".implode(", ", $array)." have correct sequence of ".$sequence." number";
} else {
	echo "No, ".implode(", ", $array)." don't have sequence of ".$sequence." number";
}
?>

Example #2 is_sequence() examples

<?php
$array = array(1.4, 1.2, 0.9, 0.7, 0.5);
$sequence = 0.2;

var_dump(is_sequence($array, $sequence, SEQUENCE_NEGATIVE));
?>

The above example will output:

bool(false)

is_sequence.php

<?php
define('SEQUENCE_POSITIVE', 1);
define('SEQUENCE_NEGATIVE', 0);

/**
 * is_sequence conception in PHP
 * 
 * @param $array array with numbers to validation.
 * @param int|float $sequence sequence number to validation.
 * @param int $flag Set if number sequence is positive or negative.
 * @return bool return true if array sequence is correct, false otherwise.
 */
function is_sequence(Array $array, $sequence, $flag = SEQUENCE_POSITIVE) {
    if (!is_numeric($sequence)) {
        throw new Exception('$sequence param need to be numeric');
    }

    $decimal = strrpos($sequence, '.') !== false ? (strlen($sequence) - strrpos($sequence, '.') - 1) : 0;

    if ($flag === SEQUENCE_NEGATIVE) {
        $array = array_reverse($array);
    }

    for ($i = 0; $i < count($array); $i++) {
        if ($array[$i + 1] && (number_format($array[$i] + $sequence, $decimal) != number_format($array[$i + 1], $decimal)))
            return false;
    }

    return true;
} 

test.php

<?php
require('is_sequence.php');

$array = array(1.4, 1.2, 1.0, 0.8, 0.6);
$sequence = 0.2;
var_dump(is_sequence($array, $sequence, SEQUENCE_NEGATIVE)); // true

$array = array(0.0002, 0.0017, 0.0032, 0.0047); 
$sequence = 0.0015;
var_dump(is_sequence($array, $sequence)); // true

$array = array(-10, -9, -8, -7, -6, -5, -4); 
$sequence = 1;
var_dump(is_sequence($array, $sequence)); // true    

$array = array(-36, -24, -12, 0, 12, 24, 36);
$sequence = 12;
var_dump(is_sequence($array, $sequence)); // true

$array = array(36, 24, 12, 0, -12, -24, -36);
$sequence = 12;
var_dump(is_sequence($array, $sequence, SEQUENCE_NEGATIVE)); // true    

$array = array(1.4, 1.2, 1.0, 1.0, 0.8, 0.6);
$sequence = 0.2;
var_dump(is_sequence($array, $sequence, SEQUENCE_NEGATIVE)); // false

$array = array(0.0002, 0.0017, 0.0026, 0.0047); 
$sequence = 0.0015;
var_dump(is_sequence($array, $sequence)); // false

$array = array(-10, -9, 8, -7, -6, -5, -4); 
$sequence = 1;
var_dump(is_sequence($array, $sequence)); // false    

// This will depend on the precision of floating point sequence, because 0.00325557 can be FALSE and 0.00321067 can be TRUE
$array = array(0.0002, 0.0017, 0.00325557, 0.0047); 
$sequence = 0.0015;
var_dump(is_sequence($array, $sequence)); // false