subtract array values from each other creating new array

Question

On my site I have the following code, which grabs values from a form and creates a text file with a list of my image paths and duration times. --

/*
This is for looping through the uploaded pictures
and sorting them and creating a text file.
*/

$vid_pix = get_post_meta($v_Id, 'vid_pix', false);

$data = "ffconcat version 1.0";
$line = '';

        usort( $vid_pix, function( $a, $b ){
            $aPor = (int) get_post_meta( $a, 'photo_order', true );
            $bPor = (int) get_post_meta( $b, 'photo_order', true );

            if ( $aPor === $bPor ) {
                return 0;
            }

            return ( $aPor < $bPor ) ? -1 : 1;
        } );

// this function removes the first value and shifts the array back so that key 1 = value 2, etc.

$Pt2 = [];
$n = count( $vid_pix );
for ( $i = 0, $j = 1; $i < $n; $i++, $j++ ) {
    $Pt2[] = ( $n === $j ) ? '6' :
        get_post_meta( $vid_pix[ $j ], 'photo_time', true );
}

        foreach ($vid_pix as $i => $vP ) {

$filename = basename( get_attached_file( $vP ));
$Por = get_post_meta($vP, 'photo_order', true);
$Pt = $Pt2[ $i ];

// try to determine the pic of the placeholder image
if ($vP === end($vid_pix))
        $last_img = $thepath.'/'.$filename;

// THIS IS THE LINE THAT OUTPUTS THE NUMBERS I NEED
$slide_dur = "\r\nduration ".$Pt;

$line .= "file '".$thepath."/".$filename."'".$slide_dur."\r\n"; 

// LAST LINE OF CONCAT TEXT FILE
$lastline = "file '".$last_img."'\r\nduration 2\r\nfile '".$last_img."'";

// PUT TOGETHER ALL THE LINES FOR THE TEXT FILE
$txtc = $data."\r\n".$line.$lastline;

// SAVE THE TEXT FILE
file_put_contents($thepath.'/paths.txt', $txtc);

Then the output using 5, 10, 13, 16, 6 looks like this --

ffconcat version 1.0
file 'home1.png'
duration 5
file 'home2.png'
duration 10
file 'home3.png'
duration 13
file 'home4.png'
duration 16
file 'home5.png'
duration 6 // last number in regards to my question
file 'home5.png'
duration 2
file 'home5.png'

What I need to do though is subtract each value with the value before it, and making a new value for that key. The values will always be dynamic.

So first key - 5 would stay 5, it would stay the same.

The second key - 10, will become 5 because 10-5.

Then the third key - 13, will become 3 because 10-13.

The fourth key - 16, will become 3 because 16-13.

Im not sure if I explained that right so if any more details are needed let me know.

Could you please add the corresponding data structures? It is very hard to read the code when you have no clue what each variable is. But I guess, you would need to replace $Pt = $Pt2[ $i ] by something like $Pt = $i == 0 ? $Pt2[ $i ] : $Pt2[$i] - $Pt2[$i - 1]. — Nico Schertler
– Nico Schertler, Commented Sep 24, 2018 at 18:04
@NicoSchertler your suggestion seems to do the trick, however how can I make it so that the last number (in this example 6) is never affected, since I have it as a static value? — 730wavy
– 730wavy, Commented Sep 25, 2018 at 0:26

IceMetalPunk · Accepted Answer · 2018-09-24 18:15:50Z

0

Shouldn't be too hard; I'm not sure where the confusion is. If you want to subtract, just subtract? So instead of outputting $Pt, just output $Pt - $Pt2[$i-1]. You'll probably want to add a condition to just use $Pt if $i === 0.

answered Sep 24, 2018 at 18:15

IceMetalPunk

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