Changing array of numbers into array of objects jq - arrays

Question

I'm totally brand new to JSON and jq so this might seem like a simple question.
I'd like to change an array of numbers into an array of objects with a key for each value (number).
Let's say I have a JSON file like this:
{
"foo": [1519739200, 1519739600, 1519740000]
}
Then my desired output would be:
{
"foo": [
{
"id": 1519739200
},
{
"id": 1519739600
},
{
"id": 1519740000
},
]
}
So far everything I've seen was connected with adding new keys with values to existing object or merging two arrays into few objects. I know that I can add more keys into already existing object but how can I add keys to an array? I assume I have to change array elements into objects first but how do I do it?
Thank you for answer.

Answer 1

Check this,
https://jqplay.org/s/xF9DyVbhXD
{ foo : [ { id : .foo[] } ] }

Answer 2

There are a few ways to go about it.
First you want to create a new object for each item in foo:
$ jq -c '{ id: .foo[] }'
{"id":1519739200}
{"id":1519739600}
{"id":1519740000}
You can then rebuild the "shape" you had - first with [ ... ]
$ jq -c '[ { id: .foo[] } ]'
[{"id":1519739200},{"id":1519739600},{"id":1519740000}]
Then the { foo: }
$ jq -c '{ foo: [ { id: .foo[] } ] }'
{"foo":[{"id":1519739200},{"id":1519739600},{"id":1519740000}]}
Another option is to use |= to modify/update .foo directly.
$ jq -c '.foo |= [{id: .[]}]'
{"foo":[{"id":1519739200},{"id":1519739600},{"id":1519740000}]}