How to select a subset of properties in a list of objects

Thank you for showing me jsonformatter.org, it is helpful. It is interesting that when I do this:

I go from this:
image

to this:

image

This means tha I manage to do (1) above, ie. iterate over the first array/list, for each element X in the array, but the variable erases prior elements X and keeps the last one. At least I can hop down a step in the array structure, which is promising.

Then I want to make it iterate over each element X but keeping each element, as you suggest, so that the screenshot above looks like:

array [1]
0 {23}
1 {21}

So then I try a small step forward:

but I get this error:

{
    "code": 0,
    "message": "Cannot read property 'concat' of undefined",
    "errorData": {}
}

If I go further and do this


I get the same error.

I also tried

and got

{
    "code": 0,
    "message": "j.map is not a function",
    "errorData": {}
}

I also tried

and got

200 - OK
Body: []

Any thoughts?