Using array_diff(), how to get difference from array2 instead of array1?

Question

I'm trying to use array_diff like so. Here are my two array outputs:

List 1 Output

Array ([0] => 0022806 )

List 2 Output

Array ([0] => 0022806 [1] => 0023199 )

PHP

$diff = array_diff($list_1, $list_2);

print "DIFF: " . count($diff) ."<br>";
print_r($diff);

The Output is:

DIFF: 0
Array ( )

Any idea what I'm doing wrong? Why is 0023199 not returned?

What if you invert the arguments? Returns an array containing all the entries from array1 that are not present in any of the other arrays. — Damien Pirsy
– Damien Pirsy, Commented Oct 16, 2012 at 18:44

Mark Baker · Accepted Answer · 2012-10-16 18:45:11Z

23

The order of arguments in array_diff() is important

Returns an array containing all the entries from array1 that are not present in any of the other arrays

answered Oct 16, 2012 at 18:45

Mark Baker

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2 Comments

user1216398 Over a year ago

Is there a better way? I have no idea what the order may look like...I'm just interested in getting the delta between the two.

Mark Baker Over a year ago

Do array_diff() both ways round, then array_merge() the results? That will give you teh entries that are in one array or the other, but not in both

Mete Yarıcı · Accepted Answer · 2016-03-30 09:56:19Z

16

try;

$diff = array_merge(array_diff($list_1, $list_2), array_diff($list_2, $list_1));

print "DIFF: " . count($diff) ."<br>";
print_r($diff);

answered Mar 30, 2016 at 9:56

Mete Yarıcı

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Comments

JRL · Accepted Answer · 2012-10-16 18:45:59Z

2

From the docs:

Returns an array containing all the entries from array1 that are not present in any of the other arrays.

If you only want to check whether they are the same, you can use $list1 == $list_2

answered Oct 16, 2012 at 18:45

JRL

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Comments

Landon · Accepted Answer · 2012-10-16 18:46:51Z

1

Per the documentation, the values of the second array are subtracted from the first one. Or, to put it another way, you start with the first array, and then remove all the values that appear in the second array. That would correctly yield an empty array that you see above

You might want to play around with intersection, that might help you get what you want.

answered Oct 16, 2012 at 18:46

Landon

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