How to access IdDict with keys?

New to Julia
1

Hi, I am trying to access the content of following object named grads:

IdDict{Any, Any} with 5 entries:
  :(Main.tmp_test_in_1)     => Float32[0.0401479 0.0100483 … -0.0744916 -0.0; 0…
  :(Main.tmp_param)         => RefValue{Any}((d_in = nothing, d_hidden = nothin…
  :(Main.n_ode)             => (model = nothing, p = nothing, re = nothing, tsp…
  Float32[-0.144463, 0.184… => Float32[-0.00789103, 0.00715096, 0.00734046, 0.0…
  Param(25, 16, 8, 10, 3, … => RefValue{Any}((d_in = nothing, d_hidden = nothin…

and when I access values with a key like this:

grads[:(Main.tmp_test_in_1)]

I got following error:

KeyError: key :(Main.tmp_test_in_1) not found

I also tested grads[:tmp_test_in_1], but I got the same error. Does anyone know what the keys should be and how to access value in this case?

Thank you!

2

Why are you using an IdDict? The keys for that are based on object identity (===) but you are creating new objects for the getindex call.

1 Like
3

The IdDict probably came from Zygote.

All of the keys you see as escaped symbols (e.g. :(Main.tmp_test_in_1)) are local or global variables that were in scope and participated in gradient calculation. So to index grads with them, use grads[tmp_test_in_1] directly. Ideally, however, you should be passing in anything you want to take the gradient of like this:

f(a, b) = ...
grad_arg1, grad_arg2 = gradient(f, arg1, arg2)

Or like this:

f(a, b) = ...
gs = gradient(() -> f(arg1, arg2), params(arg1, arg2))
grad_arg1, grad_arg2 = gs[arg1], gs[arg2]

This is covered in detail in Basics · Flux. I would highly recommend anyone new to Flux or Zygote to read through this first.