Add Get The First Item For Every Top-Level Key as a jq TIL

jq/get-the-first-item-for-every-top-level-key.md

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+# Get The First Item For Every Top-Level Key
+
+Let's say we have a JSON object where each key in that object is tied to a
+large array of values. To get a better idea of what the data looks like, we
+want to trim down the JSON a bit. Essentially, we want to tie each key to the
+first value in each of their respective arrays.
+
+We can do this by reducing the object into a new object where each top-level
+key is tied to the first item in its array.
+
+```bash
+$ jq '. as $object | reduce keys[] as $k ({}; .[$k] = $object[$k][0])' data.json
+```
+
+This uses variables (`$object` and `$k`) and the [`reduce`
+function](https://stedolan.github.io/jq/manual/#Reduce) to iterate over the
+incoming JSON object and produce a new object with the trimmed down data.
+
+JSON like this:
+
+```json
+{
+  "key1": ["a", "b", "c"],
+  "key2": [1, 2, 3],
+  "key3": ["x", "y", "z"]
+}
+```
+
+will be turned into this:
+
+```json
+{
+  "key1": "a",
+  "key2": 1,
+  "key3": "x"
+}
+```