How to merge arrays from two files into one array with jq?

Although not strictly answering the question, the command below

jq -s 'flatten | group_by(.name) | map(reduce .[] as $x ({}; . * $x))' registration.json useredits.json 

generates this output:

[ { "name": "User1", "editcount": 164, "registration": "2009-04-18T21:55:40Z" }, { "name": "User2", "editcount": 150, "registration": "2010-11-17T15:09:43Z" }, { "name": "User3", "editcount": 10 } ] 

Source: jq - error when merging two JSON files "cannot be multiplied"

The following assumes you have jq 1.5 or later, and that:

• joins.jq as shown below is in the directory ~/.jq/ or the directory ~/.jq/joins/
• there is no file named joins.jq in the pwd
• registration.json has been fixed to make it valid JSON (btw, this can be done by jq itself).

The invocation to use would then be:

jq -s 'include "joins"; joins(.name)' registration.json useredits.json 

joins.jq

# joins.jq Version 1 (12-12-2017) def distinct(s): reduce s as $x ({}; .[$x | (type[0:1] + tostring)] = $x) |.[]; # Relational Join # joins/6 provides similar functionality to the SQL INNER JOIN statement: # SELECT (Table1|p1), (Table2|p2) # FROM Table1 # INNER JOIN Table2 ON (Table1|filter1) = (Table2|filter2) # where filter1, filter2, p1 and p2 are filters. # joins(s1; s2; filter1; filter2; p1; p2) # s1 and s2 are streams of objects corresponding to rows in Table1 and Table2; # filter1 and filter2 determine the join criteria; # p1 and p2 are filters determining the final results. # Input: ignored # Output: a stream of distinct pairs [p1, p2] # Note: items in s1 for which filter1 == null are ignored, otherwise all rows are considered. # def joins(s1; s2; filter1; filter2; p1; p2): def it: type[0:1] + tostring; def ix(s;f): reduce s as $x ({}; ($x|f) as $y | if $y == null then . else .[$y|it] += [$x] end); # combine two dictionaries using the cartesian product of distinct elements def merge: .[0] as $d1 | .[1] as $d2 | ($d1|keys_unsorted[]) as $k | if $d2[$k] then distinct($d1[$k][]|p1) as $a | distinct($d2[$k][]|p2) as $b | [$a,$b] else empty end; [ix(s1; filter1), ix(s2; filter2)] | merge; def joins(s1; s2; filter1; filter2): joins(s1; s2; filter1; filter2; .; .) | add ; # Input: an array of two arrays of objects # Output: a stream of the joined objects def joins(filter1; filter2): joins(.[0][]; .[1][]; filter1; filter2); # Input: an array of arrays of objects. # Output: a stream of the joined objects where f defines the join criterion. def joins(f): # j/0 is defined so TCO is applicable def j: if length < 2 then .[][] else [[ joins(.[0][]; .[1][]; f; f)]] + .[2:] | j end; j ;