Add Zip Two JSON Files Together Based On Shared ID as a jq TIL

jq/zip-two-json-files-together-based-on-shared-id.md

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+# Zip Two JSON Files Together Based On Shared ID
+
+Let's say we have JSON file (`list1.json`) that contains an array of objects.
+Maybe they represent metadata about some books. Something like this:
+
+```json
+[
+  { 'slug': 'the-subtle-knife', 'title': 'The Subtle Knife', ... },
+  { 'slug': 'all-systems-red', 'title': 'All Systems Red', ... },
+  { 'slug': 'piranesi-abc123', 'title': 'Piranesi', ... },
+  ...
+]
+```
+
+And then we have another JSON file (`list2.json`) in a similar format that
+contains an additional piece of metadata tied to each slug:
+
+```json
+[
+  { 'slug': 'the-subtle-knife', 'author': 'Philip Pullman' },
+  { 'slug': 'all-systems-red', 'author': 'Martha Wells' },
+  { 'slug': 'piranesi-abc123', 'author': 'Susanna Clarke' },
+  ...
+]
+```
+
+And we want to pull the details from the second file and combine them into the
+first file based on that shared identifier, in this case, the `slug`.
+
+Instead of copying over a ton of values manually or writing a full-fledged
+script to do this, we can use a `jq` one-liner with the `--slurpfile` flag.
+
+```
+jq --slurpfile list1 list1.json --slurpfile list2 list2.json -n '
+  $list1[] as $item1
+  | $list2[] as $item2
+  | select($item1.slug == $item2.slug)
+  | $item1 + $item2
+'
+
+[
+  { 'slug': 'the-subtle-knife', 'title': 'The Subtle Knife', 'author': 'Philip Pullman', ... },
+  { 'slug': 'all-systems-red', 'title': 'All Systems Red', 'author': 'Martha Wells', ... },
+  { 'slug': 'piranesi-abc123', 'title': 'Piranesi', 'author': 'Susanna Clarke', ... },
+  ...
+]
+```
+
+This reads in both files as lists into named variables, selects for the items
+that have matching `slug` values, and then unions those objects together. The
+result will go to standard out, but it could also be redirected into a new JSON
+file.