It's a bit hidden but you can use the same spec as the nets and layers (e.g. NetChain).

NetEncoder[{"Function", Flatten[IntegerDigits[#, 2, 8]] &, "Varying"}]

Depending on your application, you can also avoid flattening in the encoder

NetEncoder[{"Function", IntegerDigits[#, 2, 8] &, {"Varying", 8}}]

Thank you! I modified your function to support the 24 8-bit integers expanding to 192 integers as follows:

NetEncoder[{"Function", Flatten[IntegerDigits[#, 2, 8]] &, {192}}]

and the following commands indeed produce the same output:

inp = Table[RandomInteger[{0, 255}], 24];
enc = NetEncoder[{"Function", Flatten[IntegerDigits[#, 2, 8]] &, {192}}];
Flatten[IntegerDigits[inp, 2, 8]]
enc[inp]

Regards, GW

I have been trying to modify the code so that it does not raise an error. The folllowing code does NOT raise the error:

net = NetChain[{FunctionLayer[Mean], LinearLayer[256], 
   ElementwiseLayer["ReLU"], LinearLayer[16], 
   ElementwiseLayer["ReLU"], LinearLayer[16], 1}]

but the following code DOES:

map[x_] := Mean[x]
net = NetChain[{FunctionLayer[map], LinearLayer[256], 
   ElementwiseLayer["ReLU"], LinearLayer[16], 
   ElementwiseLayer["ReLU"], LinearLayer[16], 1}]

Why?

Regards, GW

I have a follow-up question on the NetEncoder "Function" syntax. In the line

enc = NetEncoder[{"Function", Flatten[IntegerDigits[#, 2, 8]] &, {192}}]

the parameter {192} seems to indicate that the output will be an integer vector of length 192. How do I specify to expect an output integer vector of variable length? I can't find documentation on this. Thank you, Bill