jq with multiple select statements and an array

Question

I've got some JSON like the following (I've filtered the output here):

[
  {
    "Tags": [
      {
        "Key": "Name",
        "Value": "example1"
      },
     {
        "Key": "Irrelevant",
        "Value": "irrelevant"
      }
    ],

    "c7n:MatchedFilters": [
      "tag: example_tag_rule"
    ],
    "another_key": "another_value_I_dont_want"
  },
  {
    "Tags": [
      {
        "Key": "Name",
        "Value": "example2"
      }
    ],

    "c7n:MatchedFilters": [
      "tag:example_tag_rule",
      "tag: example_tag_rule2"
    ]
  }
]

I'd like to create a csv file with the value within the Name key and all of the "c7n:MatchedFilters" in the array. I've made a few attempts but still can't get quite the output I expect. There's some example code and the output below:

#Prints the key that I'm after.
cat new.jq | jq '.[] | [.Tags[], {"c7n:MatchedFilters"}] | .[] | select(.Key=="Name")|.Value'
"example1"
"example2"

#Prints all the filters in an array I'm after.
cat new.jq | jq -r '.[] | [.Tags[], {"c7n:MatchedFilters"}] | .[] | select(."c7n:MatchedFilters") | .[]'
[
  "tag: example_tag_rule"
]
[
  "tag:example_tag_rule",
  "tag: example_tag_rule2"
]

#Prints *all* the tags (including ones I don't want) and all the filters in the array I'm after.
cat new.jq | jq '.[] | [.Tags[], {"c7n:MatchedFilters"}] | select((.[].Key=="Name") and (.[]."c7n:MatchedFilters"))'
[
  {
    "Key": "Name",
    "Value": "example1"
  },
  {
    "Key": "Irrelevant",
    "Value": "irrelevant"
  },
  {
    "c7n:MatchedFilters": [
      "tag: example_tag_rule"
    ]
  }
]
[
  {
    "Key": "Name",
    "Value": "example2"
  },
  {
    "c7n:MatchedFilters": [
      "tag:example_tag_rule",
      "tag: example_tag_rule2"
    ]
  }
]

I hope this makes sense, let me know if I've missed anything.

Answer 1

Your attempts are not working because you start out with [.Tags[], {"c7n:MatchedFilters"}] to construct one array containing all the tags and an object containing the filters. You are then struggling to find a way to process this entire array at once because it jumbles together these unrelated things without any distinction. You will find it much easier if you don't combine them in the first place!

You want to find the single tag with a Key of "Name". Here's one way to find that:

first(
    .Tags[]|
    select(.Key=="Name")
).Value as $name 

By using a variable binding we can save it for later and worry about constructing the array separately.

You say (in the comments) that you just want to concatenate the filters with spaces. You can do that easily enough:

(
    ."c7n:MatchedFilters"|
    join(" ")
) as $filters

You can combine all this together like follows. Note that each variable binding leaves the input stream unchanged, so it's easy to compose everything.

jq --raw-output '
    .[]|

    first(
        .Tags[]|
        select(.Key=="Name")
    ).Value as $name|

    (
        ."c7n:MatchedFilters"|
        join(" ")
    ) as $filters|

    [$name, $filters]|

    @csv

Hopefully that's easy enough to read and separates out each concept. We break up the array into a stream of objects. For each object, we find the name and bind it to $name, we concatenate the filters and bind them to $filters, then we construct an array containing both, then we convert the array to a CSV string.

We don't need to use variables. We could just have a big array constructor wrapped around the expression to find the name and the expression to find the filters. But I hope you can see the variables make things a bit flatter and easier to understand.