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POHow can I merge two complex data structures in Perl?
 

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  1. POHow can I merge two complex data structures in Perl?
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    <p>I have a config file formatted as JSON that I need to load into Perl and then partially override/extend with new settings loaded from a separate JSON file. The particular settings that might be added/changed vary, so I want to make this override as flexible as I can.</p> <p>My plan is to merge a new partial config into the existing full config object - either in JSON or as a Perl nested data structure after using decode_json. That conversion works fine.</p> <p>Is there a simple and efficient way to do this in Perl, short of recursively walking through my complex data structure and making a lot of specific comparisons? I've looked into Hash::Merge and it is mangling my data. The issue seems to be that it looks at high level key/value pairs ("config" or "bookToolbar" below) and overrides the full key/value pair at that high level. What I want is to search depth-first and override the most specific values that it can, while keeping the other key/value pairs from the original.</p> <p>For example, here is a "full" config:</p> <pre><code>{ "config" : { "bookToolbar" : { "highlights" : { "enabled" : false }, "bookmark" : { "enabled" : false } }, "pageAspectRatio" : { "width" : "432", "height" : "648" }, "highlighter" : { "sharedColor" : "#000000", "colors" : [ "#ffff00" ] } "mainMenu" : { "index" : { "dataPath" : "data/index/", "enabled" : false }, "media" : { "dataPath" : "data/media.xml", "enabled" : false }, "toc" : { "dataPath" : "data/toc.xml" }, "glossary" : { "audioPath" : "audio/glossary/", "dataPath" : "data/glossary.xml", "imagePath" : "img/glossary/", "enabled" : false } } }, "pagelist" : [{ "hasOnPageNotes" : true, "pageName" : "cover", "hasScreenReader" : false, "hasTextMarkup" : true, "hasLinks" : false, "pageId" : "cover" }, { "hasOnPageNotes" : true, "pageName" : "1", "hasScreenReader" : false, "hasTextMarkup" : true, "hasLinks" : false, "pageId" : "1" } ] } </code></pre> <p>And here is the data I want to use to partially override/extend the above:</p> <pre><code>{ "config" : { "bookToolbar" : { "bookmark" : { "enabled" : true }, "help" : { "data" : { "url" : "aGreatHelpFile.html" }, "enabled" : true }, "links" : { "enabled" : true } } }, "pagelist" : [{ "hasOnPageNotes" : true, "pageName" : "2", "hasScreenReader" : false, "hasTextMarkup" : true, "hasLinks" : false, "pageId" : "2" } ] } </code></pre> <p>My desired output would be:</p> <pre><code>{ "config" : { "bookToolbar" : { "highlights" : { "enabled" : false }, "help" : { "data" : { "url" : "aGreatHelpFile.html" }, "enabled" : true }, "bookmark" : { "enabled" : true } "links" : { "enabled" : false } }, "pageAspectRatio" : { "width" : "432", "height" : "648" }, "highlighter" : { "sharedColor" : "#000000", "colors" : [ "#ffff00" ] }, "mainMenu" : { "index" : { "dataPath" : "data/index/", "enabled" : false }, "media" : { "dataPath" : "data/media.xml", "enabled" : false }, "toc" : { "dataPath" : "data/toc.xml" }, "glossary" : { "audioPath" : "audio/glossary/", "dataPath" : "data/glossary.xml", "imagePath" : "img/glossary/", "enabled" : false } } }, "pagelist" : [{ "hasOnPageNotes" : true, "pageName" : "cover", "hasScreenReader" : false, "hasTextMarkup" : true, "hasLinks" : false, "pageId" : "cover" }, { "hasOnPageNotes" : true, "pageName" : "1", "hasScreenReader" : false, "hasTextMarkup" : true, "hasLinks" : false, "pageId" : "1" }, { "hasOnPageNotes" : true, "pageName" : "2", "hasScreenReader" : false, "hasTextMarkup" : true, "hasLinks" : false, "pageId" : "2" } ] } </code></pre>
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    1. COI'm merging with `RIGHT_PRECEDENT` and seem to be getting the result you want. Hash::Merge's documentation mentions some issues running under ActiveState Perl on Windows, or with older versions of the Clone module. Could either of those be an issue for you?
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      1. USrutter
    2. COHmm, I tried `RIGHT_PRECEDENT` with no luck, but it did sound like just want I wanted. I am indeed using the ActiveState distrib on Windows, so that may be the issue...let me try it on my Mac and see if it improves.
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      1. POHow can I merge two complex data structures in Perl?
      1. USuptownnickbrown
    3. COSo using `Hash::Merge` with `RIGHT_PRECEDENT` did work perfectly on my Mac...and after updating Clone to the latest release ([Clone-0.34](http://search.cpan.org/~rdf/Clone-0.23/Clone.pm)) it works on Windows as well! Thanks for the tip to revisit that behavior option.
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