PHP How to get random element from multidimensional array?

Question

Say I have the following array:

$var = array( 
"green" => array("one", "two"), 
"red" => array("three", "four"),
"yellow" => array("five", "six")
);

What code would I need to write to generate a random output of any of the numbers?

I've tried the following, which will give me either "one", "three" or "five".

$section = array_rand($var);
echo $var[$section][0];

However I can't seem to randomise the key, so it will randomly choose a colour, and then randomly choose a number within that colour. I'm obviously having a dim moment. Can anyone enlighten me? Thanks.

sergio · Accepted Answer · 2014-01-26 14:03:00Z

11

The short way to get random element in that case:

$var = array( 
"green" => array("one", "two"), 
"red" => array("three", "four"),
"yellow" => array("five", "six")
);

$section = array_rand($var); //here yoy get random first of array(green or red or yellow)
echo $var[$section][array_rand($var[$section])]; //here you get random element of this array

edited Jan 26, 2014 at 14:03

answered Jan 26, 2014 at 13:57

sergio

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2 Comments

Whitenoise Over a year ago

Thanks for this, nicely explained as well.

sergio Over a year ago

Hope it will be usefull)

Eugen Rieck · Accepted Answer · 2014-01-26 14:02:37Z

8

array_rand() will randomize the complete array. This means it will

consume much entropy
Use quite a lot of CPU horsepower, if the array is large
create a copy of the array, using up RAM.

So I prefer

function getrandomelement($array) {
  $pos=rand(0,sizeof($array)-1);
  $res=$array[$pos];
  if (is_array($res)) return getrandomelement($res);
  else return $res;
}

and ofcourse

echo getrandomelement($var);

EDIT

In case this is not clear, the above function will work for any dimension, even with different sizes (non-square/cube).

answered Jan 26, 2014 at 14:02

Eugen Rieck

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5 Comments

Marty McVry Over a year ago

Wonderful solution! (Love the recursivity.)

Whitenoise Over a year ago

This doesn't work with the above array, it only works when it has keys. How could this be adapted to work with values for keys as well?

Eugen Rieck Over a year ago

Adaption is $res=$array[array_keys[$pos]]; inside the function

Whitenoise Over a year ago

I couldn't get the above to work, as when I tried $res=$array[array_keys($pos)] I got an error relating to $pos being an integer and not an array. However I've adapted what I was doing a little and so it has still been useful. Thanks.

Eugen Rieck Over a year ago

@Whitenoise It should be array_keys($array)[$pos]

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