Add Count Each Collection In A JSON Object as a jq TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1286 TILs and counting..._
+_1288 TILs and counting..._
 
 ---
 
@@ -485,6 +485,8 @@ _1286 TILs and counting..._
 
 ### jq
 
+- [Count Each Collection In A JSON Object](jq/count-each-collection-in-a-json-object.md)
+- [Count The Number Of Things In A JSON File](jq/count-the-number-of-things-in-a-json-file.md)
 - [Extract A List Of Values](jq/extract-a-list-of-values.md)
 - [Find All Objects With A Matching Key Value Pair](jq/find-all-objects-with-a-matching-key-value-pair.md)
 - [Reduce Object To Just Entries Of A Specific Type](jq/reduce-object-to-just-entries-of-a-specific-type.md)

jq/count-each-collection-in-a-json-object.md

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+# Count Each Collection In A JSON Object
+
+Let's say your JSON file is an object that represents several different
+collections (arrays) of data.
+
+```json
+{
+  "users": [ ... ],
+  "orders": [ ... ],
+  "carts": [ ... ]
+}
+```
+
+We can get a nice summary of the counts of those collections using
+[`jq`](https://stedolan.github.io/jq/). We can do that with the [`with_entries`
+function](https://stedolan.github.io/jq/manual/#to_entries,from_entries,with_entries).
+We preserve the key (name) of each collection and then process each list with
+the `length` function.
+
+```bash
+jq '. | with_entries({ "key": .key, "value": (.value | length)})' data.json
+{
+  "users": 1234,
+  "orders": 5432,
+  "carts": 89
+}
+```
+
+The `with_entries` function essentially maps over each key-value pair
+processing it with the given expression. It will then convert that `{"key":
+some_key, "value": 123}` mapping back into a key-value pair that gets combined
+with all the others.
+
+[source](https://til.simonwillison.net/jq/flatten-nested-json-objects-jq)

jq/count-the-number-of-things-in-a-json-file.md

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+# Count The Number Of Things In A JSON File
+
+JQ is a great tool for finding out the number of things in a JSON file.
+
+If the top-level contents of the JSON is a list, then you can pipe it directly
+to the [`length` function](https://stedolan.github.io/jq/manual/#length).
+
+```bash
+// [1, 2, {"three": 4}]
+$ jq '. | length' data.json
+3
+```
+
+It works the same for counting the number of entries (key-value pairs) in a
+top-level JSON object.
+
+```bash
+// { "hello": "world", "list": [1,2,3] }
+$ jq '. | length' data.json
+2
+```
+
+If you are trying to get the count of a nested value, navigate to it and then
+pipe that to `length`.
+
+```bash
+// { "hello": "world", "list": [1,2,3] }
+$ jq '.list | length' data.json
+3
+```
+
+You can even count each value in a JSON object by transforming it into an array
+of the values with `[]`.
+
+```bash
+// { "hello": "world", "list": [1,2,3] }
+$ jq '.[] | length' data.json
+5
+3
+```
+
+Notice, the length of `"world"` is `5` characters and the length of `[1,2,3]`
+is `3` elements.