Extending TensorBoardLogger

It is possible to change TensorBoardLogger's behaviour when logging specific types. Internally, when an object o::T is logged to TensorBoard with the tag name, the function preprocess(name, val, objects) is called, with objects being an iterable collection of Pair{String,Any}.

The preprocess function is responsible for converting o to or more objects of simpler types, and pushing them with their tag to the objects collection.

At the end of this step, every pair in objects will be logged to a specific backend, according to the following rules:

• ::AbstractVector{<:Real} -> Histogram backend as a vector

<!– - ::Tuple{AbstractVector,AbstractVector} Histogram backend as an histogram –>

• ::Real -> Scalar backend
• ::AbstractArray{<:Colorant} -> Image backend
• ::Any -> Text Backend

To achieve that, preprocess(name, o::T, obj) calls recursively into itself with simpler types. For example, complex numbers are converted to the real and imaginary part by the following function:

preprocess(name, val::Complex, data) = push!(data, name*"/re"=>real(val), name*"/im"=>imag(val))

To give an example, consider the following structure representing a quantity

struct LinkedQuantities
  name_1::String
  val_1
  name_2::String
  val_2
end

cost_fun = LinkedQuantities("Loss", 0.5+0.1im, "Loss_Variance", 0.01+0.02im)

and consider that you want to log objects of this type so that it logs val_1 with the tag name_1 and val_2 with tag name_2. To achieve that, one defines

function preprocess(name, val::LinkedQuantities, data)
  preprocess(val.name_1, val.val_1, data)
  preprocess(val.name_2, val.val_2, data)
end