Displaying and Randomising php Arrays

Question

I have an array displaying results as below:

Array
(
    [0] => 71
    [1] => 56
    [2] => 64
    [3] => 82
    [4] => 90
    [5] => 80
    [6         


        

Answer 1

$rand5 = array_rand(array_flip($show), 5);
// we need array_flip because array_rand returns the keys

http://php.net/array_rand

http://php.net/array_flip

Answer 2

Try this:

$arr=array();
for ($i=0;$i<5;$i++)
{
$arr[i]=$items[array_rand($items)];
}

$arr contains the result

Answer 3

Not sure on the query that gets this, but you could also possibly use

SELECT number
FROM SomeTable
ORDER BY RAND()
LIMIT 5

However note that ORDER BY RAND() is quite inefficient and as such only suitable when you are dealing with a small number of rows. However if you are bringing back a large number of rows then doing it in PHP would also be inefficient.

There are more efficient ways of returning a single random row, so if you had a very large number of rows it could be worth using efficiently retrieving a single row 5 times and unioning the results together (although you need to take account of the possibility that the random rows could be duplicates.

For example (and not really that happy with this):-

(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
UNION
(SELECT r1.number
FROM SomeTable AS r1 
INNER JOIN 
(
    SELECT RAND( ) * ( MAX( number ) - MIN( number ) ) + MIN( number ) AS number
    FROM SomeTable
) AS r2
ON r1.number >= r2.number
ORDER BY r1.number ASC
LIMIT 1)
LIMIT 5

SQL fiddle here:-

http://sqlfiddle.com/#!2/14caa/4

This is getting 10 random rows and then using a further LIMIT 5 to get only 5 rows. Of course there is still the small possibility that this might not get 5 rows (unlikely, but it is possible that every one of those unioned queries would return the same row)

Answer 4

I would go with shuffle to randomize the arrays, as per getting the 5 elements of teh array, it really depends on your need, what do you exactly want to accomplish, getting the first 5 elements, the last ones, or some other logic.