Select objects based on value of variable in object using jq - json

Question

I have the following json file:
{
"FOO": {
"name": "Donald",
"location": "Stockholm"
},
"BAR": {
"name": "Walt",
"location": "Stockholm"
},
"BAZ": {
"name": "Jack",
"location": "Whereever"
}
}
I am using jq and want to get the "name" elements of the objects where 'location' is 'Stockholm'.
I know I can get all names by
cat json | jq .[] | jq ."name"
"Jack"
"Walt"
"Donald"
But I can't figure out how to print only certain objects, given the value of a sub key (here: "location" : "Stockholm").

Answer 1

Adapted from this post on Processing JSON with jq, you can use the select(bool) like this:
$ jq '.[] | select(.location=="Stockholm")' json
{
"location": "Stockholm",
"name": "Walt"
}
{
"location": "Stockholm",
"name": "Donald"
}

Answer 2

To obtain a stream of just the names:
$ jq '.[] | select(.location=="Stockholm") | .name' json
produces:
"Donald"
"Walt"
To obtain a stream of corresponding (key name, "name" attribute) pairs, consider:
$ jq -c 'to_entries[]
| select (.value.location == "Stockholm")
| [.key, .value.name]' json
Output:
["FOO","Donald"]
["BAR","Walt"]

Answer 3

I had a similar related question: What if you wanted the original object format back (with key names, e.g. FOO, BAR)?
Jq provides to_entries and from_entries to convert between objects and key-value pair arrays. That along with map around the select
These functions convert between an object and an array of key-value
pairs. If to_entries is passed an object, then for each k: v entry in
the input, the output array includes {"key": k, "value": v}.
from_entries does the opposite conversion, and with_entries(foo) is a
shorthand for to_entries | map(foo) | from_entries, useful for doing
some operation to all keys and values of an object. from_entries
accepts key, Key, name, Name, value and Value as keys.
jq15 < json 'to_entries | map(select(.value.location=="Stockholm")) | from_entries'
{
"FOO": {
"name": "Donald",
"location": "Stockholm"
},
"BAR": {
"name": "Walt",
"location": "Stockholm"
}
}
Using the with_entries shorthand, this becomes:
jq15 < json 'with_entries(select(.value.location=="Stockholm"))'
{
"FOO": {
"name": "Donald",
"location": "Stockholm"
},
"BAR": {
"name": "Walt",
"location": "Stockholm"
}
}

Answer 4

Just try this one as a full copy paste in the shell and you will grasp it.
# pass the multiline string to the jq, use the jq to
# select the attribute named "card_id"
# ONLY if its neighbour attribute
# named "card_id_type" has the "card_id_type-01" value.
# jq -r means give me ONLY the value of the jq query no quotes aka raw
cat << EOF | \
jq -r '.[]| select (.card_id_type == "card_id_type-01")|.card_id'
[
{ "card_id": "id-00", "card_id_type": "card_id_type-00"},
{ "card_id": "id-01", "card_id_type": "card_id_type-01"},
{ "card_id": "id-02", "card_id_type": "card_id_type-02"}
]
EOF
# this ^^^ MUST start first on the line - no whitespace there !!!
# outputs:
# id-01
or with an aws cli command
# list my vpcs or
# list the values of the tags which names are "Name"
aws ec2 describe-vpcs | jq -r '.| .Vpcs[].Tags[]
|select (.Key == "Name") | .Value'|sort -nr
Note that you could move up and down in the hierarchy both during the filtering phase and during the selecting phase :
kubectl get services --all-namespaces -o json | jq -r '
.items[] | select( .metadata.name
| contains("my-srch-string")) |
{ name: .metadata.name, ns: .metadata.namespace
, nodePort: .spec.ports[].nodePort
, port: .spec.ports[].port}
'