How to swap key and value of an object using jq? - json

Question

Using jq I would like to inverse a json object so that the property becomes the value and the value becomes the key.
Source:
{
"123": "Foobar"
"567": "Poit"
}
Goal:
{
"Foobar": "123"
"Poit": "567"
}
How can I achieve that?

Answer 1

In your particular case:
to_entries | map( {(.value) : .key } ) | add
More robustly:
to_entries | map( {(.value|tostring) : .key } ) | add
Or if you prefer:
with_entries( .key as $k | .key = (.value|tostring) | .value = $k )
Caveat: all these are potentially lossy.

Answer 2

If some keys have equal values then probably you would like to get an array of keys as value:
to_entries
| map( {(.value) : {(.key):null} } )
| reduce .[] as $item ({}; . * $item)
| to_entries
| map({key:.key, value:(.value|keys)})
| from_entries
input:
{
"key1": "val0",
"key2": "val1",
"key3": "val1"
}
output:
{
"val0": ["key1"],
"val1": ["key2", "key3"]
}

Answer 3

I would use an approach similar to #peak's answer but without using the add method
First use to_entries to get an output like this:
-> to_entries
Output:
[
{
"key": "123",
"value": "Foobar"
},
{
"key": "567",
"value": "Poit"
}
]
Then use map to swap the keys with values:
-> to_entries | map({key: .value|tostring, value: .key}) ###**tostring** method converts a number to string since keys can't be numbers
Output:
[
{
"key": "Foobar",
"value": "123"
},
{
"key": "Poit",
"value": "567"
}
]
Finally use from_entries to remove the key/value and return back to the original format:
-> to_entries | map({key: .value|tostring, value: .key}) | from_entries
Output:
{
"Foobar": "123",
"Poit": "567"
}