jq count the number of items in json by a specific key

Question

The following is the first two items in my json file

{
"ReferringUrl": "N",
"OpenAccess": "0",
"Properties": {
    "ItmId": "1694738780"
   }
}
{
"ReferringUrl": "L",
"OpenAccess": "1",
"Properties": {
    "ItmId": "1347809133"
  }
}

I want to count the number of items by each ItmId appeared in the json. For example, items that with "ItmId" 1694738780 appears 10 times and items with "ItmId" 1347809133 appears 14 times in my json file. Then return a json like this

{"ItemId": "1694738780",
 "Count":  10
}
{"ItemId": "1347809133",
 "Count":  14
}

I am using bash. And prefer do this totally by jq. But it's ok to use other method.

Thank you!!!

Answer 1

Here's a super-efficient solution -- in particular, no sorting is required. The following implementation requires a version of jq with inputs but it is easy to adapt the program to use earlier versions of jq. Please remember to use the -n command-line option if using the following:

# Count the occurrences of distinct values of (stream|tostring).
# To avoid unwanted collisions, or to recover the exact values,
# consider using tojson
def counter(stream):
  reduce stream as $s ({}; .[$s|tostring] += 1);

counter(inputs | .Properties.ItmId)
| to_entries[]
| {ItemId: (.key), Count: .value}

Answer 2

Using jq command

cat json.txt | jq '.Properties .ItmId' | sort | uniq -c | awk -F " " '{print "{\"ItmId\":" $2 ",\"count\":" $1"}"}'| jq .