Processing Arrays with Loops in SORACOM Flux

Disclosure based on the operational standards for "Representations that are difficult for general consumers to distinguish as representations of a business operator": This article was written by an employee of SORACOM, INC. as of the date of publication. However, it is a personal post and does not represent the official statements or views of SORACOM, INC.

What I want to do

I will share some tips for processing arrays using loops in SORACOM Flux.
In a previous blog post, I mentioned that it is difficult to handle arrays of unknown length in SORACOM Flux, but I found that this can be solved by using loops.

How to do it

Let's configure SORACOM Flux.
If you are wondering "What is SORACOM Flux?", please check here.

Configuration Overview

We will create a flow that performs the following.
The numbers correspond to the balloon numbers in the diagram above explaining the flow.

0. Trigger settings
   Event source: API/Manual Execution
   Output channel: API Channel
   Since we are confirming the loop functionality this time, we select API/Manual Execution.
   In actual applications, please select an appropriate trigger.

1. Simple Object Detection Action
   Input channel: API Channel

   Configuration of the API Action block

   Settings

   Major Item	Detailed Item	Setting Value	Remarks
   CONDITION	Action execution condition	(Blank)
   CONFIG	Image URL	https://blog.soracom.com/ja-jp/wp-content/uploads/2024/07/soracam-team-1-1024x683.jpg	Image borrowed from SORACOM official blog
   OUTPUT	Send action output to another channel	Enabled
   OUTPUT	Destination channel	Output	Channel name is arbitrary

   Configuration screen (example)
   

   Output JSON

   {
     "person": 6,
     "car": 0,
     "bus": 0,
     "truck": 0,
     "cat": 0,
     "dog": 0,
     "objects": [
       {
         "location": [
           0.6609779,
           0.17652985,
           0.9373262,
           0.9943735
         ],
         "score": 0.8904824,
         "label": "person",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.37141305,
           0.3185921,
           0.5251937,
           0.969292
         ],
         "score": 0.8751769,
         "label": "person",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.04004524,
           0.21790065,
           0.21095791,
           0.84099317
         ],
         "score": 0.8547369,
         "label": "person",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.4620108,
           0.37004647,
           0.6945141,
           0.9970469
         ],
         "score": 0.83913076,
         "label": "person",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.23511018,
           0.3791213,
           0.39225024,
           0.8577786
         ],
         "score": 0.8179504,
         "label": "person",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.13871717,
           0.3871962,
           0.27425474,
           0.8432603
         ],
         "score": 0.7499229,
         "label": "person",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.4429141,
           0.47117797,
           0.48522377,
           0.6288479
         ],
         "score": 0.2793063,
         "label": "tie",
         "ts": "2025-05-07T01:48:41Z"
       },
       {
         "location": [
           0.39311492,
           0.4475629,
           0.42104053,
           0.6097326
         ],
         "score": 0.2578054,
         "label": "tie",
         "ts": "2025-05-07T01:48:41Z"
       }
     ]
   }
   

   Output channel: Output

2. Set loop counter (num), loop limit (length), and the array to decompose

   Input channel: Output

   Configuration of the Republish block

   Input payload

   {
     "person": 6,
     "car": 0,
     "bus": 0,
     "truck": 0,
     "cat": 0,
     "dog": 0,
     "objects": [···]
   }
   

   *The content of objects is omitted.

   Settings

   Major Item	Detailed Item	Setting Value	Remarks
   CONDITION	Action execution condition	(Blank)
   CONFIG	Transform data	✅️
   CONFIG	Content Type	application/json	Default setting
   CONFIG	Content	{000a "num" : 0,000a "length" : ${len(payload.objects)},000a "objects" : ${payload.objects}000a}	Calculate the length of the array output in objects.000aInclude len() within ${}.000aIt might be tempting to write len(${payload.objects}), but that is incorrect.
   OUTPUT	Send action output to another channel	Enabled
   OUTPUT	Destination channel	Output Channel

   

   Output JSON

   {
       "num":0,
       "length":8,
       "objects":[···]
   }
   

   *The content of objects is omitted.

   Output channel: Output Channel

3. num increment and extraction of the num-th element of payload.objects
   Input channel: Output Channel

   Configuration of the Republish block

   {
       "num":0,
       "length":8,
       "objects":[···]
   }
   

   *The content of objects is omitted.

   Settings

   Major Item	Detailed Item	Setting Value	Remarks
   CONDITION	Action execution condition	payload.num < payload.length - 1	Perform increment and output when the condition on the left is met.
   CONFIG	Transform data	✅️
   CONFIG	Content Type	application/json	Default setting
   CONFIG	Content	{ "num":${payload.num+1}, "length": ${payload.length}, "objects": ${payload.objects} }	Increment the input num and output. Write the increment +1 inside ${}. Output length and objects as they are.
   OUTPUT	Send action output to another channel	Enabled
   OUTPUT	Destination channel	Output Channel	Loop by returning to the input channel of this action

   {
       "num":1,
       "length":8,
       "objects":[···]
   }
   

   *The content of objects is omitted.

   Output channel: Output Channel (same as the input channel for this action)

4. Notify the num-th element
   Input channel: Output Channel

   Configuration of the Slack notification action

   Input payload

   {
       "num":0,
       // Incremented as 1, 2, 3, 4... and entered
       "length":8,
       "objects":[···]
   }
   

   Settings

   Major Item	Detailed Item	Setting Value	Remarks
   CONDITION	Action execution condition	(Blank)
   CONFIG	URL	URL starting with https://hooks.slack.com/services	Obtain the webhook URL by referring to the method here (Japanese documentation).
   CONFIG	Payload	${payload.num} : ${payload.objects[payload.num]}	Put the number on the 1st line and the num-th element of payload.objects on the 2nd line.
   OUTPUT	Send action output to another channel	Disabled

   

Execution Results

Notifications are sent to SORACOM's Slack as shown below.
However, it seems the order in which notifications arrive in Slack is unordered.
Caution is needed for applications that are sensitive to the order of the array and the arrival order of requests.

Note that since the execution condition payload.num < payload.length - 1 was set for the Republish action where the loop was applied, this became the upper limit for the number of loops. However, if this condition is removed, the loop is designed to stop at 10 times.
If you want to process an array with a length of 10 or more, I think you will be able to process each element by creating another Republish action setting to connect to the Output channel in parallel, setting the initial value of num to 10, and running the loop.

{
    "num" : 10,
    "length" : ${len(payload.objects)},
    "objects": ${payload.objects}
}