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Json – Can the following jq recipe be simplified

Using jq version 1.5, I need to conditionally output some json objects (in an array) based on a value within the nested object. I’ve looked here on StackOverflow and managed to get what I want working, but I wonder if it can be simplified. Here’s my data

{
  "data": [
    {
      "name": "Rich",
      "age": 10
    },
    {
      "name": "Michael",
      "age": 11
    },
    {
      "name": "Victoria",
      "age": 8
    },
    {
      "name": "Philip",
      "age": 9
    }
  ]
}

and I need to reproduce the same structure, but only for pupils 10 or older, so the output should look like this:

{
  "data": [
    {
      "name": "Rich",
      "age": 10
    },
    {
      "name": "Michael",
      "age": 11
    }
  ]
}

I have the following code which achieves what I want:

.data | to_entries | map(select(.value.age>9)) | [.[].value] | {data: .}

but I read in the jq manual that with_entries can be used to replace to_entries -> map -> from_entries, now I’m not using from_entries, but it made me question whether I should be, and if it would mean I don’t need to manually recreate my array and object in the last two pipes.

Is this the best way to solve this type of problem?

I tried using using from_entries after my map, to see if that did what I need, but I got an error:

jq: error (at <stdin>:19): Cannot use number (0) as object key

So my understanding of how that works isn’t correct.

Tags:

2

Answers


  1. 0 
    .data |= map(select(.age >= 10))

    Will produce the same output in a more cleaner way as you can test in this online demo.

    Using the |= update assignment to update the value of .data.

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  2. 0

    You already have an array, so you don’t need to convert to entries first. Simply map the array and select the required elements:

    .data |= map(select(.age >= 10))

    Alternatively

    .data | { data: map(select(.age >= 10)) }

    or

    { data: (.data | map(select(.age >= 10))) }

    Calling to_entries on an array will give you a new array with a key-value object, the key being the index:

    [
  {
    "key": 0,
    "value": {
      "name": "Rich",
      "age": 10
    }
  },
  ...
]

    So unless your condition needs to perform calculations on the index (say, selecting every 3rd element, or only those indices which are multiples of 5), you don’t need to_entries here.

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