JQ sorting key by arbitrary order - json

Question

I am trying to sort by key in an arbitrary format (key 'event' should be the first)
I know this one sort the key by alphabetical order:
jq -S '.' file.json
but is there a function to sort key so that the first one is always the same and not by alphabetical order?
It is to make them more human readable and have the most significant key first
Currently have:
{key1:value, shouldbeFirstKey:value2, ...}
Would like
{shouldbeFirstKey:value2, key1:value, ...}

Answer 1

Suppose we have an object with a bunch of keys, and want some of those keys to appear in a certain order, while leaving the others as-is. Then the technique illustrated by the following example can be used:
$ jq -n '{a:2,b:3,first:0,second:1} | . as $in | {first,second} + $in'
The result:
{
"first": 0,
"second": 1,
"a": 2,
"b": 3
}
rekey
Let's call the object defining the key ordering as the "template object" ({first,second} above). Notice that using the technique described above, the keys in the "template object" always appear in the result. If we only want the template object keys to appear in the result if they appear in the input, we can modify the above approach using the following function:
def rekey(obj):
. as $in
| reduce (obj|keys_unsorted)[] as $k ({};
if $in|has($k) then . + {($k): $in[$k]} else . end)
| . + $in ;
For example:
{a:2,b:3,first:0,second:1} | rekey({first,second,third})
produces:
{
"first": 0,
"second": 1,
"a": 2,
"b": 3
}
With walk/1
If one wants to reorder keys recursively, one can use walk/1 (defined as at https://github.com/stedolan/jq/blob/master/src/builtin.jq),
as illustrated here using the above definition of rekey:
walk(if type == "object" then rekey($template) else . end)
where $template represents the "template object".
There is no need to define a special variant of walk/1. Simply define a function that takes as input an arbitrary object, and that produces the desired reordering.
(If your jq comes with the version of walk/1 that uses keys, then you should consider updating your jq, or redefine walk/1 to use keys_unsorted.)

Answer 2

Here is a filter (derived from walk/1 [source]) which will reorder the keys of subobjects using a function:
def reorder(order):
. as $in
| if type == "object" then
reduce (keys_unsorted|order)[] as $key(
{}; . + { ($key): ($in[$key] | reorder(order)) }
)
elif type == "array" then map( reorder(order) )
else .
end;
the order function is expected to return the set of keys in whatever order is desired. e.g. the following function moves "shouldbeFirstKey" to the first position
def neworder:
"shouldbeFirstKey" as $s
| index($s) as $i
| if $i==null then . else [$s] + .[:$i] + .[$i+1:] end
;
so that
{key1:"value", shouldbeFirstKey:"value2", other:{key3:"value3", shouldbeFirstKey:"value4"}}
| reorder(neworder)
produces the output
{
"shouldbeFirstKey": "value2",
"key1": "value",
"other": {
"shouldbeFirstKey": "value4",
"key3": "value3"
}
}
Try it online!

Answer 3

idea from #jq170727 's answer:
jq '
def reorder(a; n):
def order(a; n):
a as $a |
n as $n |
index($a) as $i |
if $i == null then .
else
if $i<$n then .[:$i] + .[$i+1:$n+1] + [$a] + .[$n+1:]
elif $n<$i then .[:$n] + [$a] + .[$n:]
else .
end
end;
. as $in
| if type == "object" then
reduce (keys_unsorted|order(a;n))[] as $key(
{}; . + { ($key): ($in[$key] | reorder(a; n)) }
)
elif type == "array" then map( reorder(a; n) )
else .
end;
[.[] | reorder("id"; 0)| reorder("size"; 3) | reorder("name"; 1)]'
data.json