php array_merge without erasing values?

Question

Background: Trevor is working with a PHP implementation of a standard algorithm: take a main set of default name-value pairs, and update those name-value pairs, but only for those name-value pairs where a valid update value actually exists.

Problem: by default, PHP array_merge works like this ... it will overwrite a non-blank value with a blank value.

$aamain   =   Array('firstname'=>'peter','age'=>'32','nation'=>'');
$update   =   Array('firstname' => '','lastname' => 'griffin', age =>'33','nation'=>'usa');

print_r(array_merge($aamain,$update));    
/*
Array
(
    [firstname] =>           // <-- update set this to blank, NOT COOL!
    [age] => 33              // <-- update set this to 33, thats cool
    [lastname] => griffin    // <-- update added this key-value pair, thats cool
    [nation] => usa          // <-- update filled in a blank, thats cool.
)
*/

Question: What's the fewest-lines-of-code way to do array_merge where blank values never overwrite already-existing values?

print_r(array_coolmerge($aamain,$update));    
/*
Array
(
    [firstname] => peter  // <-- don't blank out a value if one already exists!
    [age] => 33
    [lastname] => griffin
    [nation] => usa

)
*/

UPDATE: 2016-06-17T11:51:54 the question was updated with clarifying context and rename of variables.

Answer 1

If you also want to keep the values that are blank in both arrays:

array_filter($foo) + array_filter($bar) + $foo + $bar

Answer 2

This will put duplicates into a new array, I don't know if this is what you want though.

<?php
  $foobar =   Array('firstname' => 'peter','age' => '33',);
  $feebar =   Array('firstname' => '','lastname' => 'griffin',);
  $merged=$foobar;
  foreach($feebar as $k=>$v){
    if(isset($foobar[$k]))$merged[$k]=array($v,$foobar[$k]);
    else $merged[$k]=$v;
  }
  print_r($merged);
?>

This will simply assure that feebar will never blank out a value in foobar:

<?php
  $foobar =   Array('firstname' => 'peter','age' => '33',);
  $feebar =   Array('firstname' => '','lastname' => 'griffin',);
  $merged=$foobar;
  foreach($feebar as $k=>$v) if($v)$merged[$k]=$v;
  print_r($merged);
?>

or ofcourse,

<?
  function cool_merge($array1,$array2){
    $result=$array1;
    foreach($array2 as $k=>$v) if($v)$result[$k]=$v;
    return $result;
  }

  $foobar =   Array('firstname' => 'peter','age' => '33',);
  $feebar =   Array('firstname' => '','lastname' => 'griffin',);
  print_r(cool_merge($foobar,$feebar));
?>

Answer 3

Adjust to your needs:

# Replace keys in $foo
foreach ($foo as $key => $value) {
    if ($value != '' || !isset($bar[$key])) continue;
    $foo[$key] = $bar[$key];
}

# Add other keys in $bar
# Will not overwrite existing keys in $foo
$foo += $bar;

Answer 4

Try this:

$merged = array_map(
    create_function('$foo,$bar','return ($bar?$bar:$foo);'),
    $foobar,$feebar
);

Not the most readable solution, but it should replace only non-empty values, regardless of which order the arrays are passed..

Answer 5

array_replace_recursive($array, $array2);

This is the solution.

Answer 6

Well, if you want a "clever" way to do it, here it is, but it may not be as readable as simply doing a loop.

$merged = array_merge(array_filter($foo, 'strval'), array_filter($bar, 'strval'));

edit: or using +...