jq - setpath - Cannot index object with number - json

Question

I would like to add new path into existing document
./jq < test.json
{
"correlationId": "6298865a73b477106c98d021",
"leg": 0,
"tag": "sent",
"offset": 322858,
"len": 178,
"prev": {
"page": {
"file": 10352,
"page": 2
},
"record": 911
},
"data": "HTTP/1.1 403 Forbidden\r\nDate: Fri, 16 Feb 2018 08:37:54 GMT\r\nServer: \r\nConnection: close\r\nX-CorrelationID: Id-6298865a73b477106c98d021 0\r\nContent-Type: text/html\r\n\r\nAccess Denied"
}
I am using filter setpath described in jq manual.
But even if I copied the documented string
./jq 'setpath([0,"a"]; 1)' < test.json
still getting error:
jq: error (at <stdin>:1): Cannot index object with number
I do not see there any syntax issue. Did I overlooked something?
Regards and thanks, Reddy

Answer 1

You cannot use integer indices as keys in the JSON object. For JSON objects, the key must be a string, so you could write:
jq 'setpath(["0","a"]; 1)' < test.json
Output:
{
"correlationId": "6298865a73b477106c98d021",
"leg": 0,
"tag": "sent",
"offset": 322858,
"len": 178,
"prev": {
"page": {
"file": 10352,
"page": 2
},
"record": 911
},
"data": "HTTP/1.1 403 Forbidden\r\nDate: Fri, 16 Feb 2018 08:37:54 GMT\r\nServer: \r\nConnection: close\r\nX-CorrelationID: Id-6298865a73b477106c98d021 0\r\nContent-Type: text/html\r\n\r\nAccess Denied",
"0": {
"a": 1
}
}