PHP work out difference between two values in while loop

Question

I'm outputting an XML document with PHP from mysql results, in one column I have a bunch of values, but these are accumulative values, i.e.: 1,3,6,8,12,45,etc...but how can I only echo out the difference between values rather than the values themselves in this:

while($row = mysql_fetch_array($result)){
    $strXML .= "<set name='".date("G:i:s", strtotime($row["tstamp"]))
            .  "' value='".$row['steam']."' color='AFD8F8' />";
}

The column in question is "steam", how could I go about doing this?

What is the result you expect? Give some sample input and the corresponding output. — Vincent Mimoun-Prat
– Vincent Mimoun-Prat, Commented Jan 21, 2011 at 11:04
1,3,6,8,12,45, this would be might raw mysql data but i would want 2,3,2,4,33...by the way i can do simple math but its just doing it within the while loop i'm struggling with — benhowdle89
– benhowdle89, Commented Jan 21, 2011 at 11:05

Floern · Accepted Answer · 2011-01-21 11:09:46Z

1

Do you want to do this?

$previous = 0;
while($row = mysql_fetch_array($result)){
    $difference = $row['steam'] - $previous;
    $strXML .= "<set name='".date("G:i:s", strtotime($row["tstamp"]))
            .  "' value='".$difference."' color='AFD8F8' />";
    $previous = $row['steam'];
}

assuming $row['steam'] is a single number, not a comma separated list.

answered Jan 21, 2011 at 11:09

Floern

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Mark Baker · Accepted Answer · 2011-01-21 11:05:36Z

1

$dataArray = explode(',',$row['steam']);
$dataCount = count($dataArray);
$newArray = array();
for($i = 1; $i < $dataCount; $i++) {
   $newArray[] = $dataArray[$i] - $dataArray[$i-1];
}
$newData = implode(',',$newArray);

answered Jan 21, 2011 at 11:05

Mark Baker

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3 Comments

benhowdle89 Over a year ago

brilliant so, $newData is essentially my $row array?

Mark Baker Over a year ago

$newData is essentially $row['steam'], not the entire $row array... you have other entries in $row such as $row["tstamp"]

benhowdle89 Over a year ago

oh ok. so what i would do is: value='".$newData."'

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