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.

the standard behavior for handling duplicates is fine: the key-value pair in feebar will overwrite the corresponding key-value pair in foobar. The only difference I want is to never let feebar blank out a value in foobar. — dreftymac
– dreftymac, Commented Apr 27, 2009 at 13:40
See also (python-based) stackoverflow.com/questions/38987/… — dreftymac
– dreftymac, Commented Dec 28, 2016 at 19:26
See also (python-based) stackoverflow.com/q/6354436/42223 — dreftymac
– dreftymac, Commented Jan 1, 2017 at 21:23
See also (php zeroes) stackoverflow.com/questions/14134006/… — dreftymac
– dreftymac, Commented Apr 18, 2018 at 15:30

Matt · Accepted Answer · 2009-04-27 13:55:55Z

16

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 +...

answered Apr 27, 2009 at 13:55

Matt

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2 Comments

dreftymac Over a year ago

Thanks for that one. Avoiding a loop can be seen as a kind of "useless cleverness" on some level perhaps -- but it's just nice to not have to always use loops when something like map, select, or a list comprehension (as implemented in some other languages) seems more concise.

too much php Over a year ago

Using 'trim' instead of 'strval' will also clear out items which only contain whitespace.

Calvin · Accepted Answer · 2009-04-27 14:20:27Z

5

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..

edited Apr 27, 2009 at 14:20

answered Apr 27, 2009 at 14:14

Calvin

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Comments

timo · Accepted Answer · 2016-03-14 15:19:41Z

4

array_replace_recursive($array, $array2);

This is the solution.

edited Mar 14, 2016 at 15:19

timo

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answered Mar 14, 2016 at 14:20

Center Developments

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4 Comments

Jonas Czech Over a year ago

While this code snippet may solve the question, including an explanation really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion.

GRowing Over a year ago

I agree, this is the best solution here. No explanation needed. PHP documentation is sufficient.

Tum Over a year ago

Am I missing something or isn't this at all what OP asked? OP's result using this answer would be: { ["firstname"] => "", ["age"] => "33", ["nation"] => "usa", ["lastname"] => "griffin" }

viion Over a year ago

This is NOT the solution, this will overwrite existing values. onlinephp.io/c/cfb52

soulmerge · Accepted Answer · 2009-04-27 14:14:15Z

4

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;

answered Apr 27, 2009 at 14:14

soulmerge

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Comments

Russ · Accepted Answer · 2009-09-29 09:12:56Z

2

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

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

answered Sep 29, 2009 at 9:12

Russ

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Comments

elzapp · Accepted Answer · 2009-04-27 14:05:51Z

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));
?>

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