I have spent an embarrassing amount of time trying to achieve something that I believe should be quite trivial.

The question is about JSONata because I want to use this in the context of an AWS Step Function.

Let's say I have an array with some stats, each coming, say, from the execution of a separate process. In my real case, it will come from a Map Step.

Importantly, I do not know which stats are coming in; I do not have a pre established list of possible stat keys.

[{
    "stat1": 2,
    "stat2": 3 
},
{
    "stat1": 4,
    "stat3": 5
}]

I would like to use JSONata to aggregate those, so that each different stat is aggregated using sum, to basically obtain something like this:

{
    "stat1": 6,
    "stat2": 3,
    "stat3": 5
}

I have spent an embarrassing amount of time trying to achieve something that I believe should be quite trivial.

The question is about JSONata because I want to use this in the context of an AWS Step Function.

Let's say I have an array with some stats, each coming, say, from the execution of a separate process. In my real case, it will come from a Map Step.

Importantly, I do not know which stats are coming in; I do not have a pre established list of possible stat keys.

[{
    "stat1": 2,
    "stat2": 3 
},
{
    "stat1": 4,
    "stat3": 5
}]

I would like to use JSONata to aggregate those, so that each different stat is aggregated using sum, to basically obtain something like this:

{
    "stat1": 6,
    "stat2": 3,
    "stat3": 5
}

• amazon-web-services
• aws-step-functions
• jsonata

2 Answers 2

Does this work?

$spread(){ $keys($): $sum($.*) }

First, it splits all objects's keys into separate arrays, then groups them based on the key and aggregates the values.

JSONata Playground: https://jsonatastudio/playground/8a13fa7e

I'm not sure but I am thinking >>>

(
  $keys := $distinct($.*.$keys());
  $reduce($keys, {}, function($result, $key) {
    $result{$key} := $sum($.[*][$key]);
    $result
  })
)

It just gets all unique keys first, then adds up the value for each key across all objects no need to know the stat names beforehand