How can I run 2 loops together in PHP without duplicating values? - php

Question

I'm trying to check MD5 of some data with md5 some files, both of them are stored in one dimensional arrays. Say I have 4 files in the $files array with the same number of $datas, the following code prints "NO DIFFERENCE" 12 times instead of 4 times.
foreach($files as $file) {
foreach($datas as $data) {
if(md5($data) !== md5_file($file)) {
echo "NO DIFFERENCE";
}
}
}
How do I prevent duplicating a loop?
Update:
Both arrays $datas and $files contains equal number of values but the tricky part is the values in $files array starts from key number 2 (because I removed "." and ".." from scandir result) whereas in $datas array values start from key number 0.

Answer 1

the following code prints "NO DIFFERENCE" 12 times instead of 4 times.
The reason for that is you have a nested loop.
For each value in the $files array, your inner foreach will run once.
So say if you have 3 values in $files and 4 values in $datas, the loop will run as follows:
First value in $files iterated
Inner loop runs, and iterates through all 4 values in $datas
Second value in $files iterated
Inner loop runs, and iterates through all 4 values in $datas
Third value in $files iterated
Inner loop runs, and iterates through all 4 values in $datas

Answer 2

Try this with one loop like this :
foreach($datas as $key => $value) {
if(md5($value) !== md5_file($files[$key])) {
echo "NO DIFFERENCE";
}
}
Note: The loop work when you have same no of values for both arrays

Answer 3

If you want to compare md5(files) to the mfs5(datas) you can simply do this:
for ($i = 0; $i < sizeof($files); $i++){
if(md5($datas[$i]) !== md5_file($files[$i+2]))
echo "NO DIFFERENCE";
}
If you want to check if each file have one corresponding md5(datas) then you should use you double loop as you did.

Answer 4

First, are you sure that !== is the operator you want to use to say 'no difference' ?
If you are looking for equality, maybe you want to use ===
Second, md5(...) is time consuming, so extract the hash in a variable.
Third, if you mean equality, you can add a break in the inner loop to stop looping as soon as you find the equality.
foreach($files as $file) {
$md5File = md5_file($file); // extract in a variable
foreach($datas as $data) {
if(md5($data) === $md5File) { // === instead of !==
echo "NO DIFFERENCE";
break; // break as soon as possible
}
}
}

Answer 5

You could use a callback function. But then you should be clear about how exactly you will describe an algorithm of your problem.
The following sample shows how to maybe achieve it. But it assumes that the arrays are in the same order and that you don't want to cross-compare everything. Also array_udiff may not be the best approach for it.
function compare_by_md5($data, $file) {
if( md5($data) === md5_file($file)) {
echo "NO DIFFERENCE";
}
}
array_udiff($datas, $files, 'compare_by_md5');
Sample is shown here: http://codepad.org/lYOyCuXA

Answer 6

If you simply want to detect if there is a difference:
$dataHashes = array();
foreach($datas as $data) {
$dataHashes[md5($data)] = true;
}
$different = false;
foreach($files as $file) {
if(!isset($dataHashes[md5_file($file)])) {
$different = true;
break;
}
}
var_dump($different);
If you want to know which files are different, then:
$dataHashes = array();
foreach($datas as $data) {
$dataHashes[md5($data)] = true;
}
foreach($files as $file) {
if(!isset($dataHashes[md5_file($file)])) {
echo $file, 'is different', PHP_EOL;
}
}