Correct JSON format for CoreMotion data for ActivityClassification purposes

Question

DewG OP

Created Jul ’25

Replies 2

Boosts 0

Participants 2

I’m developing an activity classifier that I’d like to input using the JSON format of CoreMotion data.

I am getting the error:

Unable to parse /Users/DewG/Downloads/Testing/Step1/Testing.json. It does not appear to be in JSON record format. A SequenceType of dictionaries is expected

I've verified that the format I am using is JSON via various JSON validators, so I am expecting I'm just holding it wrong. Is there an example of a JSON file with CoreMotion data that I can model after?

Answered by Frameworks Engineer in 848298022

Try flattening the fields and putting them in an array like this:

[
  {
	"date" : "2025-07-09T01:24:03Z",
	"activity" : "BestActivity",
	"confidence" : 0.977258026599884,
	"id" : "A3473CBB-D3CF-4371-B150-E00BA1518BF6",
	"mlAnnotated" : true,
	"model" : "FILLTHISIN",
	"modelVersion" : "FILLTHISIN",
	"pitch" : 0.7971696055429895,
	"roll" : 0.2853617665740398,
	"yaw" : 0.9832477411686631,
	"sampleType" : "motionUpdate",
	"time" : 773703581.004733
  }, ...
]

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Answer 1

DewG OP

Jul ’25

My current data looks like:

{
	"date" : "2025-07-09T01:24:03Z",
	"samples" : [
		{
			"activity" : "BestActivity",
			"confidence" : 0.977258026599884,
			"id" : "A3473CBB-D3CF-4371-B150-E00BA1518BF6",
			"mlAnnotated" : true,
			"model" : "FILLTHISIN",
			"modelVersion" : "FILLTHISIN",
			"motionSample" : {
				"pitch" : 0.7971696055429895,
				"roll" : 0.2853617665740398,
				"yaw" : 0.9832477411686631
			},
			"sampleType" : "motionUpdate",
			"time" : 773703581.004733
		}]
}

0

Answer 2

Frameworks Engineer OP

Apple

Jul ’25

Accepted Answer

Try flattening the fields and putting them in an array like this:

[
  {
	"date" : "2025-07-09T01:24:03Z",
	"activity" : "BestActivity",
	"confidence" : 0.977258026599884,
	"id" : "A3473CBB-D3CF-4371-B150-E00BA1518BF6",
	"mlAnnotated" : true,
	"model" : "FILLTHISIN",
	"modelVersion" : "FILLTHISIN",
	"pitch" : 0.7971696055429895,
	"roll" : 0.2853617665740398,
	"yaw" : 0.9832477411686631,
	"sampleType" : "motionUpdate",
	"time" : 773703581.004733
  }, ...
]

0