Calculate mean of a range of XML Elements in PHP - php

Question

I'm trying to calculate the mean of a range of XML elements in PHP, but haven't found any solution yet.
Here are the XML elements.
<root>
<quoteDay>
<date>2018-02-26</date>
<close>1586,96</close>
</quoteDay>
<quoteDay>
<date>2018-02-23</date>
<close>1577,11</close>
</quoteDay>
<quoteDay>
<date>2018-02-22</date>
<close>1565,5</close>
</quoteDay>
</root>
Here is the PHP code:
<?php
$xml = simplexml_load_file("file.xml") or die("Error: Cannot create object");
$id = -1;
$total[] = 0;
foreach ($xml->root as $root) {
foreach ($root->quoteDay as $quoteDay) {
$id ++;
$total[] += $root->quoteDay[$id]->close;
$close = number_format(round($quoteDay->close,0));
echo $quoteDay->date; echo $close; echo $total[$id+1];
}
}
?>
So, for each quoteDay, I would like to return the date, close and a moving average.
Date 2018-02-26 would return the mean of "close" for 2018-02-26 and 2018-02-23 = (1586,96+1577,11)/2.
Mean for 2018-02-23 would return (1577,11+1565,5)/2.
I've, as you can see, tried to sum a cumulative total sum for each element, but for some reason I can't understand it won't work.
How can I accomplish calculating a moving average for the elements?

Answer 1

In order to achieve your result you need to do a couple of things:
simplexml_load_file() already gives you the root, so there's no need for your first loop
The $total array is not necessary
Your XML has , as decimal separators, but PHP uses ., so you need to replace them in order to do math and not lose the decimals (here I cast to float which can make you lose precision, look into bcmath to avoid that)
I assume that for the first day, when there's no previous, the moving average is the day's value
So, your code would look like this:
<?php
$xml = simplexml_load_file("a.xml") or die("Error: Cannot create object");
$id = 0;
foreach ($xml->quoteDay as $quoteDay) {
echo "Moving average for ".$quoteDay->date.":".PHP_EOL;
$current = (float) str_replace(",", ".", $quoteDay->close);
$previous = $xml->quoteDay[$id + 1]
? (float) str_replace(",", ".", $xml->quoteDay[$id + 1]->close)
: $current;
$movingMean = ($current + $previous) / 2;
echo $movingMean.PHP_EOL;
echo PHP_EOL;
$id++;
}
Demo
Result
Moving average for 2018-02-26:
1582.035
Moving average for 2018-02-23:
1571.305
Moving average for 2018-02-22:
1565.5
To generalize it to $daysInMovingMean days, use a for loop to get the days up to the days needed, stopping earlier if necessary (i.e. no more days left):
$xml = simplexml_load_file("a.xml") or die("Error: Cannot create object");
$id = 0;
$daysInMovingMean = 3;
foreach ($xml->quoteDay as $quoteDay) {
echo "Moving average for ".$quoteDay->date.":".PHP_EOL;
$sum = 0;
for ($days = 0; $days < $daysInMovingMean; $days++) {
if (!$xml->quoteDay[$id + $days]) break;
$sum += (float) str_replace(",", ".", $xml->quoteDay[$id + $days]->close);
}
$sumovingMean = $sum / $days;
echo $sumovingMean.PHP_EOL;
echo PHP_EOL;
$id++;
}
Notice that in this example you get the same results as before if you set $daysInMovingMean = 2;
Demo