How to extract specific field from JSON array with jq

Question

I want to process JSON data using jq. Here is an excerpt from the data:

{
  "lat": "49.3877286",
  "lon": "6.704062",
  "tag": [
    {
      "k": "name",
      "v": "Beckingen"
    },
    {
      "k": "is_in",
      "v": "Merzig-Wadern,Saarland,Bundesrepublik Deutschland,Europe"
    },
    {
      "k": "place",
      "v": "town"
    },
  ]
}
{
  "lat": "49.287307",
  "lon": "6.8827786",
  "tag": [
    {
      "k": "name",
      "v": "Püttlingen"
    },
    {
      "k": "place",
      "v": "town"
    },
    {
      "k": "population",
      "v": "18748"
    }
  ]
}

I need to extract the lat, lon, and name fields, like this:

{
  "lat": "49.3877286",
  "lon": "6.704062",
  "name": "Beckingen"
},
{
  "lat": "49.287307",
  "lon": "6.8827786",
  "name": "Püttlingen"
}

I'm almost there, but I can't figure out how to select a field from an array using select(). Can anyone point me in the right direction?

Many thanks,

Enno

peak · Accepted Answer · 2019-02-06 19:54:42Z

3

Depending on your precise requirements, you could use map(select(...)) or .[] | select(...), along the lines of, for example:

.tag[] | select(.k == "name") | .v

You might want to make this more robust, for example by taking into account the possibility that there might not be exactly one "name":

first(.tag[] | select(.k == "name") | .v // null)

edited Feb 6, 2019 at 19:54

answered Feb 6, 2019 at 16:38

peak

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Comments

peak · Accepted Answer · 2019-02-06 16:59:46Z

0

Ok, I got it:

{lat: .lat, lon: .lon, tag: .tag[]}
| select(.tag.k=="name") 
| {lat: .lat, lon: .lon, name: .tag.v}

The trick was to use .tag[] which multiplies each entry with the number of array elements in .tag, then to select the relevant entries and then to construct the output JSON. Thanks for the hint, @peak!

edited Feb 6, 2019 at 16:59

peak

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answered Feb 6, 2019 at 16:50

mcenno

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2 Comments

peak Over a year ago

You could simplify that to {lat, long, name: (.tag[] | select(.k == "name") | .v)}

mcenno Over a year ago

Cool, thanks! For the sake of completion: in this particular case it was lon, not long.

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