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String comparisons using xpath

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I have some xml (which I hate and think is the biggest waste of space in the history of computing, but I guess we have to live with it) containing image elements and I am trying to find those images updated in the last week. ie lastUpdate > 2018-03-07.


Failing miserably I tried with the simpler type attributes with similar success.


The data

<?xml version="1.0" encoding="utf-8"?>
  <item id="5018">
      <text lastUpdate="2018-03-14T01:23:04+01:00" lang="en" />
      <image type="a" lastUpdate="2018-01-05T09:26:21+01:00">
      <image type="p" lastUpdate="2018-03-09T09:26:21+01:00">
      <image type="r" lastUpdate="2018-03-09T09:26:21+01:00">

The attempts:

$xml = simplexml_load_file('test.xml');
$x = $xml->xpath("//image[@type = 'a']");      // 1 result as expected
$x = $xml->xpath("//image[@type != 'a']");     // 2 results as expected  (types p and r)
$x = $xml->xpath("//image[@type > 'a']");      // 0 results ??????

$x = $xml->xpath("//image[@lastUpdate = '2018-03-09T09:26:21+01:00']");     // 2 results

// and the similar main problem:

$x = $xml->xpath("//image[@lastUpdate > '2018-03-07']");     // 0 results ??????

Any suggestions?

Edited by Barand
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Which version of xpath do you use? Such a comparison ( >a ) was only added in v2.0. I guess it also applies to your 2nd attempt ( @lastUpdate > '2018-03-07' ) because it's actually a string comparison too.

Edited by phpmillion
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  • Solution

This seems to work:

$x = $xml->xpath("//image[number(translate(substring-before(@lastUpdate, 'T'), '-', '')) > 20180307]");

The substring-before(@lastUpdate, 'T') returns the date string that comes before the 'T'.


Then, that value is used within translate([VALUE], '-', '') to remove the dashes in the date string.


Then, that value is used within number([VALUE]) to convert the resulting string 'YYYYMMDD' into a number value and is compared against the numeric value for your specified date.


You can compare on date and time if you use '+' in the substring-before() function and use '-T:' in the second parameter for the translate() function.

Edited by Psycho
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