Merge Arrays of JSON

Question

So my objective is to merge json files obtain this format:

{
  "title": "NamesBook",
  "list": [
    {
      "name": "Ajay"
    },
    {
      "name": "Al"
    }
  ]
}

And I have files that look like this format:

blahblah.json

{
  "title": "NamesBook",
  "list": [
    {
      "name": "Ajay"
    }
  ]
}

blueblue.json

{
  "title": "NamesBook",
  "list": [
    {
      "name": "Al"
    }
  ]
}

I can store the list array of all my names in a variable with the following:

x = jq -s '.[].list' *.json

And then I was planning on appending the variable to an empty array in a file I created, out.json, which looks like this:

{
  "type": "NamesBook",
  "list": []
}

However, when my script runs over the line

jq '.list[] += "$x"' out.json'

It brings up a jq error:

Cannot iterate over null.

Even when I add a random element, the same error shows up. Tips on how I should proceed? Are there other tools in jq to help achieve merging arrays?

Answer 1

You can merge your files with add (jq 1.3+):

jq -s '.[0].list=[.[].list|add]|.[0]' *.json

or flatten (jq 1.5+):

jq -s '.[0].list=([.[].list]|flatten)|.[0]' *.json

[.[].list] - creates an array of all "list" arrays

 [
  [
    {
      "name": "Ajay"
    }
  ],
  [
    {
      "name": "Al"
    }
  ]
]

[.[].list]|flatten - flatten it (or .[].list|add - add all the arrays together)

[
  {
    "name": "Ajay"
  },
  {
    "name": "Al"
  }
]

.[0].list=([.[].list]|flatten)|.[0] - replace the first "list" with the merged one, output it.

{
  "title": "NamesBook",
  "list": [
    {
      "name": "Ajay"
    },
    {
      "name": "Al"
    }
  ]
}

Answer 2

Let me also provide just what the title asks for, because I'm sure a lot of people that stepped on this question look for something simpler.

Any of the following (added math2001 and pmf answers):

echo -e '["a","b"]\n["c","d"]' | jq -s 'add'

echo -e '["a","b"]\n["c","d"]' | jq -s 'flatten(1)'

echo -e '["a","b"]\n["c","d"]' | jq -s 'map(.[])'

echo -e '["a","b"]\n["c","d"]' | jq -s '[.[][]]'

echo -e '["a","b"]\n["c","d"]' | jq '.[]' | jq -s

results in:

[
"a",
"b",
"c",
"d"
]

Note: Also any of the above can apply to arrays of objects.

Answer 3

Assuming every file will have the same title and you're simply combining the list contents, you could do this:

$ jq 'reduce inputs as $i (.; .list += $i.list)' blahblah.json blueblue.json

This just takes the first item and adds to its list, the list of all the other inputs.