Adding elements to a MLMultiArray

Question

I have a CoreML model (created using TF and converted to CoreML). For it

input is: MultiArray (Double 1 x 40 x 3)
output is: MultiArray (Double)

I will be getting these [a,b,c] tuples and need to collect 40 of them before sending into to the model for prediction. I am looking through the MLMultiArray documentation and am stuck. May be because of I am new to Swift.

I have a variable called modelInput that I want to initialize and then as the tuples come in, add them to the modelInput variable.

modelInput = MLMultiArray(shape:[1,40,3], dataType:MLMultiArrayDataType.double))

The modelInput.count is 120 after this call. So I am guessing an empty array is created.

However now I want to add the tuples as they come in. I am not sure how to do this. For this I have a currCount variable which is updated after every call. The following code however gives me an error.

"Value of type 'UnsafeMutableRawPointer' has no subscripts"

    var currPtr : UnsafeMutableRawPointer = modelInput.dataPointer + currCount
    currPtr[0] = a
    currPtr[1] = b
    currPtr[2] = c
    currCount = currCount + 3

How do I update the multiArray?

Is my approach even correct? Is this the correct way to create a multi array for the prediction input?

I would also like to print the contents of the MLMultiArray. There doesn't appear to be any helper functions to do that though.

Matthijs Hollemans · Accepted Answer · 2020-01-02 10:17:08Z

1

You can use pointers, but you have to change the raw pointer into a typed one. For example:

let ptr = UnsafeMutablePointer<Float>(OpaquePointer(multiArray.dataPointer))
ptr[0] = a
ptr[1] = b
ptr[2] = c

answered Jan 2, 2020 at 10:17

Matthijs Hollemans

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3 Comments

Anuj Over a year ago

Hi Matthijs. I have an array of FP 32 values that I have loaded into my app using a JSON file. The shape of the array is [1, 12, 128, 192]. Then I have created an MLMultiArray as follows: let data = try? MLMultiArray(shape: [1, 12, 128, 192], dataType: .int32) So, how do I get the data into this MLMultiarray now ? Can you please provide a code example or point me in the right direction? Love your CoreML book btw. Thanks

Matthijs Hollemans Over a year ago

Since the data is already in the correct order in the array, only the datatype is different. So you can simply do a for loop to loop through the elements in the array, convert them to Int32 and put it into the MLMultiArray.

Anuj Over a year ago

Hi Matthijs, thanks for the tip. I tried this code: let yHat = try? MLMultiArray(shape: [1, 12, 128, 192], dataType: .float32) for i in 0..<12{ for j in 0..<128{ for k in 0..<192{ yHat![[0 as NSNumber, i as NSNumber, j as NSNumber, k as NSNumber]] = (self.inputData[0][i][j][k]) as NSNumber } } } but this looks like giving a wrong output i.e. a single big array of values rather than an array of arrays.

SFlow · Accepted Answer · 2020-01-02 05:41:29Z

0

I figured it out. I have to this --

    modelInput[currCount+0] = NSNumber(floatLiteral: a)
    modelInput[currCount+1] = NSNumber(floatLiteral: b)
    modelInput[currCount+2] = NSNumber(floatLiteral: c)

I cannot use the raw pointer to access elements.

answered Jan 2, 2020 at 5:41

SFlow

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