Select lots of known IDs from a big JSON document efficiently - json

Question

I am trying to get some value from json via jq in bash. With small value it work nice but with big json it work too slow, like 1 value for each 2-3 second. Example of my code:
json=$(curl -s -A "some useragent" "url" )
pid=$(cat idlist.json | jq '.page_ids[]')
for id in $pid
do
echo $pagejson|jq -r '.page[]|select(.id=='$id')|.url'>>path.url
done
The "pid" is list of id that I type before running script. It may contain 700-1000 id. Example object of json
{
"page":[
{
"url":"some url",
"id":some numbers
},
{
"url":"some url",
"id":some numbers
}
]
}
Is there any way to speed up it? In javascript it work faster than it. Example of javascript:
//First sort object with order
var url="";
var sortedjson= ids.map(id => obj.find(page => page.id === id));
//Then collect url
for ( x=0 ; x < sortedjson.length;x++) {
url+=sortedjson[x].url
};
Should I sort json like in javascript for better performance? I don't tried it because don't know how.
Edit:
Replaced "pid" variable with json to use less code and for id in $(echo $pid) with for id in $pid.
But it still slow down if id list more than about 50

Answer 1

Calling jq once per id is always going to be slow. Don't do that -- call jq just once, and have it match against the full set.
You can accomplish that by passing the entire comma-separated list of ids into your one copy of jq, and letting jq itself do the work of splitting that string into individual items (and then putting them in a dictionary for fast access)
For example:
pid="24885,73648,38758,8377,747"
jq --arg pidListStr "$pid" '
($pidListStr | [split(",")[] | {(.): true}] | add) as $pidDict |
.page[] | select($pidDict[.id | tostring]) | .url
' <<<"$pagejson"

Answer 2

The following solution uses the same approach as the one posted by Charles Duffy (*) but is only applicable:
if each of the specified id values in $pid appears at most once as an id in the JSON objects in the .page array; or
if the goal is to extract, for each id in $pid, at most one corresponding object from the .page array.
The idea is to remove an id from the dictionary once it is found, and to stop if and when all ids have been found.
jq --arg pidListStr "$pid" '
($pidListStr | [splits(" *, *") | {(.): true}] | add) as $pidDict
| label $finish
| foreach .page[] as $page ($pidDict + {emit:null};
if length == 1 then break $finish
else ($page.id | tostring) as $id
| if .[$id] then delpaths([[$id]]) | .emit = $page.url
else .emit = null
end
end;
.emit // empty )
'
(*) Caveat
Using $pidDict here assumes there are no "collisions"; this condition would hold if all the id values in the .page objects are numeric.

Answer 3

The following is a response to the original question, which posited:
pid="24885,73648,38758,8377,747"
echo $pagejson|jq -r '.page[]|select(.id=='$pid')|.url'
(Based on subsequent edits to the question, it would appear that the intent was to iterate over the id values separately, invoking jq once per value. That is a bad idea as well but can be dealt with in a separate response.)
Response to original question
There are several problems with the invocation of jq based on
interpolating $pid as was originally done.
The major problem is that your query, when expanded, includes this select statement:
select(.id==24885,73648,38758,8377,747)
whereas what you evidently intend is:
select(.id==(24885,73648,38758,8377,747))
It's not difficult to see that there's a huge difference, which affects both functionality and performance.
Since you don't give any hints about the expected input, it's not feasible to suggest how the query might be optimized. To illustrate, though, suppose it's known that the .id values in the input are distinct. Then once all the ids in the query have been found, execution can stop.
In general, passing shell variables in by string interpolation is not a great idea. Some alternatives to consider are using --arg or --argjson.

Answer 4

The following solution, which is based on the one posted by Charles
Duffy (*), can be used if each of the specified id values in $pid
appears at most once as an id in the JSON objects in the .page array.
The idea is to stop if and when all the $pid ids have been found.
This can be accomplished with the following helper function:
def first_n(stream; $n):
label $done
| foreach stream as $x (-1; .+1; if . >= $n then break $done else $x end);
The solution can then be written as follows:
($pidListStr | [splits(" *, *") | {(.): true}] | add) as $pidDict
| ($pidDict|length) as $n
| first_n(.page[] | select($pidDict[.id | tostring]) | .url; $n)
This solution is similar to the one using foreach posted elsewhere
on this page, but is simpler and probably slightly more efficient as
the dictionary, once constructed, is unaltered.
The solution using foreach, however, can also be used if the ids of the
objects in the .page array are not unique, and if the goal is to
extract, for each id in $pid, at most one corresponding object from
the .page array.
(*) Caveat
Using $pidDict here assumes there are no "collisions"; this condition would hold if all the id values in the .page objects are numeric.