Question 109616 in Json Question posted in
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How can I filter json basing on keys being in array in JQ

How can this be achieved?

Those are inputs:

ARRAY=["keyA", "keyC", "keyE"]
JSON={
  "keyA": "valueA",
  "keyB": "valueB",
  "keyC": "valueC",
  "keyD": "valueD",
  "keyE": "valueE",
  "keyF": "valueF"
}

So basing on what I have in ARRAY (keys) how can I output corresponding keys and values from JSON in order to have TARGET_JSON like this:

TARGET_JSON={
  "keyA": "valueA",
  "keyC": "valueC",
  "keyE": "valueE"
}
Tags:

4

Answers


  1. 0

    You can use the select function in jq to filter a JSON object based on the keys being in an array. for example
    jq ‘select(keys_unmatched(["name", "city"]) | not)’ file.json

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  2. 0

    This is not JSON but javascript:

    $ node
Welcome to Node.js v19.7.0.
Type ".help" for more information.
> ARRAY=["keyA", "keyC", "keyE"]
[ 'keyA', 'keyC', 'keyE' ]
> JSON={
...   "keyA": "valueA",
...   "keyB": "valueB",
...   "keyC": "valueC",
...   "keyD": "valueD",
...   "keyE": "valueE",
...   "keyF": "valueF"
... }
{
  keyA: 'valueA',
  keyB: 'valueB',
  keyC: 'valueC',
  keyD: 'valueD',
  keyE: 'valueE',
  keyF: 'valueF'
}
> 
> var j = {}
> ARRAY.forEach(elt => j[elt] = JSON[elt] )
> console.log(j)
{ keyA: 'valueA', keyC: 'valueC', keyE: 'valueE' }
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  3. 0 
    jq —-argjson a "$ARRAY" '
  def project($a): . as $in
  | reduce $a[] as $k (null;.[$k] =$in[$k]); 
  project($a)' <<< "$JSON"
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  4. 0

    Here is one possible solution using reduce:

    . as $obj
| reduce ["keyA", "keyC", "keyE"][] as $key (
    {}; .[$key] = $obj[$key]
)

    Or with user-provided variables:

    jq --argjson keys '["keyA", "keyC", "keyE"]' '. as $obj
| reduce $keys[] as $key ({}; .[$key] = $obj[$key])

    If you don’t care about the order of keys in the result (there is no inherent meaning to order of keys in JSON objects, because they are a bag of key-value pairs without order), then an alternative would be using with_entries, although it will be slower for large inputs:

    jq --argjson keys '["keyA", "keyC", "keyE"]' 'with_entries(select(.key | IN($keys[])))'

    but this could be avoided by building a lookup/index object first:

    jq --argjson keys '["keyA", "keyC", "keyE"]' 'INDEX($keys[]; .) as $keys
| with_entries(select(.key | in($keys)))'
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