Resolved this on github:

.[0] as $keys |
.[1] as $values |
reduce range(0; $keys|length) as $i  ( {}; . + { ($keys[values[$i] })

This was actually relatively straight forward:

.things | .[] | {name: .name, category: .params | .[] | select(.key=="category") | .value }

The |= .+ part in the filter adds a new element to the existing array. You can use jq with filter like:

jq '.data.messages[3] |= . + {
      "date": "2010-01-07T19:55:99.999Z", 
      "xml": "xml_samplesheet_2017_01_07_run_09.xml", 
      "status": "OKKK", 
      "message": "metadata loaded into iRODS successfullyyyyy"
}' inputJson

To avoid using the hardcoded length value 3 and dynamically add a new element, use . | length which returns the length, which can be used as the next array index, i.e.,

jq '.data.messages[.data.messages| length] |= . + {
      "date": "2010-01-07T19:55:99.999Z", 
      "xml": "xml_samplesheet_2017_01_07_run_09.xml", 
      "status": "OKKK", 
      "message": "metadata loaded into iRODS successfullyyyyy"
}' inputJson

(or) as per peak's suggestion in the comments, using the += operator alone

jq '.data.messages += [{
     "date": "2010-01-07T19:55:99.999Z",
     "xml": "xml_samplesheet_2017_01_07_run_09.xml", 
     "status": "OKKK", 
     "message": "metadata loaded into iRODS successfullyyyyy"
}]'

which produces the output you need:

{
  "report": "1.0",
  "data": {
    "date": "2010-01-07",
    "messages": [
      {
        "date": "2010-01-07T19:58:42.949Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "OK",
        "message": "metadata loaded into iRODS successfully"
      },
      {
        "date": "2010-01-07T20:22:46.949Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "NOK",
        "message": "metadata duplicated into iRODS"
      },
      {
        "date": "2010-01-07T22:11:55.949Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "NOK",
        "message": "metadata was not validated by XSD schema"
      },
      {
        "date": "2010-01-07T19:55:99.999Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "OKKK",
        "message": "metadata loaded into iRODS successfullyyyyy"
      }
    ]
  }
}

Use jq-play to dry-run your jq-filter and optimize any way you want.

If your input is a stream of objects, then unless your jq has inputs, the objects must be "slurped", e.g. using the -s command-line option, in order to combine them.

Thus one way to combine objects in the input stream is to use:

jq -s add

For the second problem, creating an array:

jq -s .

There are of course other alternatives, but these are simple and do not require the most recent version of jq. With jq 1.5 and later, you can use 'inputs', e.g. jq -n '[inputs]'

Efficient solution

For the first problem (reduction), rather than slurping (whether via the -s option, or using [inputs]), it would be more efficient to use reduce with inputs and the -n command-line option. For example, to combine the stream of objects into a single object:

jq -n 'reduce inputs as $in (null; . + $in)'

Equivalently, without --null-input:

jq 'reduce inputs as $in (.; . + $in)'

One way would be to add the objects together with the .roles array and delete it after

.categories[][].resources[] |= ( 
  . + { readRole: .roles[0], writeRole: .roles[1] } | del(.roles)
)

^{jqplay demo}

map( { (.name|tostring): . } ) | add

(The tostring is for safety/robustness.)

INDEX/1

If your jq has INDEX/1 (introduced in version 1.6), you can simply write:

INDEX(.name)

jq can deal with multiple input arrays. You can pipe the whole output of the loop to it:

for service in "$services" ; do
    curl "$service/path"
done | jq -r '.[]|[.id,.startDate,.calls]|@csv'

Note that the csv transformation can be done by @csv

This trick with the jq 1.5 inputs streaming filter seems to do it

... | jq -n '.items |= [inputs]'

Ex.

$ find ~/ -maxdepth 1 -name "D*" | 
    while read line; do 
      jq -n --arg name "$(basename "$line")" \
            --arg path "$line" \
        '{name: $name, path: $path}'
    done | jq -n '.items |= [inputs]'
{
  "items": [
    {
      "name": "Downloads",
      "path": "/home/steeldriver/Downloads"
    },
    {
      "name": "Desktop",
      "path": "/home/steeldriver/Desktop"
    },
    {
      "name": "Documents",
      "path": "/home/steeldriver/Documents"
    }
  ]
}

Use slurp mode:

  o   --slurp/-s:

      Instead of running the filter for each JSON object
      in the input, read the entire input stream into a large
      array and run the filter just once.

$ jq -s '.' < tmp.json
[
  {
    "name": "John",
    "email": "[email protected]"
  },
  {
    "name": "Brad",
    "email": "[email protected]"
  }
]