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

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1351 TILs and counting..._
+_1352 TILs and counting..._
 
 ---
 
@@ -505,6 +505,7 @@ _1351 TILs and counting..._
 - [Get The First Item For Every Top-Level Key](jq/get-the-first-item-for-every-top-level-key.md)
 - [Reduce Object To Just Entries Of A Specific Type](jq/reduce-object-to-just-entries-of-a-specific-type.md)
 - [Turn A List From A Command Into JSON](jq/turn-a-list-from-a-command-into-json.md)
+- [Zip Two JSON Files Together Based On Shared ID](jq/zip-two-json-files-together-based-on-shared-id.md)
 
 ### Kitty
 

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

@@ -0,0 +1,52 @@
+# 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.