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

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.

$ jq '. as $object | reduce keys[] as $k ({}; .[$k] = $object[$k][0])' data.json

This uses variables ($object and $k) and the reduce function to iterate over the incoming JSON object and produce a new object with the trimmed down data.

JSON like this:

{
  "key1": ["a", "b", "c"],
  "key2": [1, 2, 3],
  "key3": ["x", "y", "z"]
}

will be turned into this:

{
  "key1": "a",
  "key2": 1,
  "key3": "x"
}