Conditionally add values to JSON arrays

Question

I have some JSON objects that I need to add a value to if it doesn't already exist.

Each object will be the following except the contact_group inside each array (1-5) will vary:

{
  "contact_groups": {
    "1": [
      "/contact_group/78"
    ],
    "2": [
      "/contact_group/79"
    ],
    "3": [],
    "4": [],
    "5": []
  }
}

I want to add /contact_group/109 to each array if it doesn't already exist, so the above would become:

{
  "contact_groups": {
    "1": [
      "/contact_group/78",
      "/contact_group/109"
    ],
    "2": [
      "/contact_group/79",
      "/contact_group/109"
    ],
    "3": [
      "/contact_group/109"
    ],
    "4": [
      "/contact_group/109"
    ],
    "5": [
      "/contact_group/109"
    ]
  }
}

I'm pretty sure jq can do this, but I'm inexperienced with it, so I don't know where to begin. Does anyone know how/if this can be done?

Inian · Accepted Answer · 2020-07-16 17:22:57Z

2

You can use with_entries() function on the parent element to convert the sub elements into a pair keyed by key and value and add the string to value array, if it doesn't have it already

jq '.contact_groups |= ( with_entries( if ( .value | index("/contact_group/109") | not ) then .value += [ "/contact_group/109" ] else . end ) )'

The with_entries(..) builtin is a shorthand for doing to_entries | map | from_entries. The index("/contact_group/109") | not part ensures to add the entry if the string is not already present in the .value array.

^{See demo on jqplay}

edited Jul 16, 2020 at 17:22

answered Jul 16, 2020 at 17:17

Inian

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Kusalananda · Accepted Answer · 2025-02-20 09:38:03Z

A variation of Inian's answer, but without the with_entries() call, with parametrization of the string we're adding, and with some minor simplifications to the logic:

$ jq --arg str '/contact_group/109' '.contact_groups |= map_values(if index($str) then . else . + [$str] end)' file
{
  "contact_groups": {
    "1": [
      "/contact_group/78",
      "/contact_group/109"
    ],
    "2": [
      "/contact_group/79",
      "/contact_group/109"
    ],
    "3": [
      "/contact_group/109"
    ],
    "4": [
      "/contact_group/109"
    ],
    "5": [
      "/contact_group/109"
    ]
  }
}

Another way to do this without the if statement is to use select() to only add stuff to the ones which index() returns null for:

jq --arg str '/contact_group/109' '.contact_groups |= map_values(select(index($str) == null) += [$str])' file

Assuming that the ordering of the bottom-level arrays is unimportant, we can be a bit more "sloppy" and add the string to all arrays while applying unique to remove duplicates:

$ jq --arg str '/contact_group/109' '.contact_groups |= map_values(. += [$str] | unique )' file
{
  "contact_groups": {
    "1": [
      "/contact_group/109",
      "/contact_group/78"
    ],
    "2": [
      "/contact_group/109",
      "/contact_group/79"
    ],
    "3": [
      "/contact_group/109"
    ],
    "4": [
      "/contact_group/109"
    ],
    "5": [
      "/contact_group/109"
    ]
  }
}

With a string that is already present in some arrays:

$ jq --arg str '/contact_group/79' '.contact_groups |= map_values(. += [$str] | unique )' file
{
  "contact_groups": {
    "1": [
      "/contact_group/78",
      "/contact_group/79"
    ],
    "2": [
      "/contact_group/79"
    ],
    "3": [
      "/contact_group/79"
    ],
    "4": [
      "/contact_group/79"
    ],
    "5": [
      "/contact_group/79"
    ]
  }
}

This approach would be useful if you'd wanted to add many strings to the arrays:

$ jq '.contact_groups |= map_values(. += $ARGS.positional | unique )' --args '/contact_group/79' '/contact_group/89' '/contact_group/99' <file
{
  "contact_groups": {
    "1": [
      "/contact_group/78",
      "/contact_group/79",
      "/contact_group/89",
      "/contact_group/99"
    ],
    "2": [
      "/contact_group/79",
      "/contact_group/89",
      "/contact_group/99"
    ],
    "3": [
      "/contact_group/79",
      "/contact_group/89",
      "/contact_group/99"
    ],
    "4": [
      "/contact_group/79",
      "/contact_group/89",
      "/contact_group/99"
    ],
    "5": [
      "/contact_group/79",
      "/contact_group/89",
      "/contact_group/99"
    ]
  }
}

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