Merge arrays with control of array position - php

Question

I have two random arrays merged, everything displaying/functioning beautifully. The one stuck I have is this:
When I merge the two arrays together I need to make sure that every 3 item comes from array2.
array1 (a,b,c,d,e,f,g,h,i,j,k)
array2 (a1,a2,a3,a4)
My desired outcome:
d k c a1 j i g a2 etc.
What I have done so far:
function randomize_blocks($arr, $num = 1) {
shuffle($arr);
$r = array();
for ($i = 0; $i < $num; $i++) {
$r[] = $arr[$i];
}
return $num == 1 ? $r[0] : $r;
}
//gather donor blocks into an array
$donorBlocks = array($blockA, $blockB, $blockC, $blockD, $blockE, $blockF,
$blockG, $blockH, $blockI, $blockJ, $blockK, $blockL, $blockM, $blockN,
$blockO);
//gather value blocks into an array
$valueBlocks = array($valueA, $valueB, $valueC, $valueD);
//shake that shuffler real hard! DT
$shuffled_valueBlocks = randomize_blocks($valueBlocks, 4);
$shuffled_donorBlocks = randomize_blocks($donorBlocks, 15);
//combine our shuffled arrays together
$combinedArrays = array_merge($shuffled_valueBlocks, $shuffled_donorBlocks);
//shuffle them all together!
$shuffled_blocks = randomize_blocks($combinedArrays, 19);
//display bocks on page
foreach ($combinedArrays as $key => $value) {
echo $value;
}
What is the best way to accomplish this?

Answer 1

Here is a way with array_splice to modify the longest of the two arrays into the desired result:
$a = ['a', 'b', 'c', 'd'];
$b = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15];
foreach ($a as $i => $v)
array_splice($b, $i*4+3, 0, [$v]);
$b will be:
[1, 2, 3, 'a', 4, 5, 6, 'b', 7, 8, 9, 'c', 10, 11, 12, 'd', 13, 14, 15]

Answer 2

What about something like this?
$a1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l'];
$a2 = ['a1', 'a2', 'a3', 'a4'];
$a = [];
shuffle($a1);
foreach ($a1 as $k => $v) {
$a[] = $v;
if (($k + 1) % 3 === 0 && $a2) $a[] = array_shift($a2);
}

Answer 3

This is based on the assumption that you want both arrays shuffled as well as placed in your desired pattern:
$array_one = array('a','b','c','d','e','f','g','h','i','j','k');
$array_two = array('a1','a2','a3','a4');
function merge_random_interval($array_one = array(), $array_two = array(), $interval = 3) {
$return_array = array();
// Shuffle the arrays - that seems to be important?
shuffle($array_one);
shuffle($array_two);
// Go through the first array
$array_two_index = 0;
for ($i = 0; $i < count($array_one); $i++) {
// Every $interval add a value from the second array
if ($i > 0 && $i % $interval == 0) {
// Make sure there is a value in the second array
if (isset($array_two[$array_two_index])) {
$return_array[] = $array_two[$array_two_index];
$array_two_index++;
}
}
$return_array[] = $array_one[$i];
}
// You may want to check if $array_two has more values that weren't added?
// Compare $array_two_index against count($array_two)
return $return_array;
}
$result_array = merge_random_interval($array_one, $array_two, 3);
echo implode(' ', $result_array); // g d c a1 h i j a4 b e a a2 k f