JQ

Select the elements where an attribute is equal to a value

jq '.[] | select(.location=="Stockholm")' json

Select the elements with a regex

jq '.[] | select(.location|test("Sto.+olm"))

Count elements in array

jq '. | length'

Source

Delete long arrays

Help to get headers, and clear the infos

jq 'del(.data.long_array[]?)' json_file

Select multiple fields

jq '.[] | .login, .id'

source

Select based on key entries

echo '{"key1":{"o1": "v1"},"key2":{"o2":"v2"}}' | jq 'with_entries(select(.key == "key2"))'
{
  "key2": {
    "o2": "v2"
  }
}

Unique elements

echo '[{"o1": "v1"},{"o1":"v1"},{"o1":"v2"}]' | jq '[.[].o1] | unique'
[
  "v1",
  "v2"
]

Replace and/or transform a value

echo '[{"o1": "1"},{"o1":"2"},{"o1":"3","o2":"untouched"}]' | jq '.[].o1 |= (. | tonumber + 100)'
[
  {
    "o1": 101
  },
  {
    "o1": 102
  },
  {
    "o1": 103,
    "o2": "untouched"
  }
]