Array(chn) drops third dimension for nchain==1

[bgctw]

This behavior of Array(chn) dropping the third dimension when only a single chain is present was unexpected to me. Is it meant to be this way?
It breaks code that uses mapslices on the Array over the third dimension, e.g. for computing an output for each sample, that does not check the special case of only a single chain before.

Minimal working example:

chn2 = Chains(rand(3, 2, 1), [:a, :b]); 
size(chn2)                  # 3-dimensional
size(Array(chn2))       # only 2-dimensional

[devmotion]

Yes, it is intended:

MCMCChains.jl/src/constructors.jl

Line 54 in 82def13

return to_matrix(chn)

By default, all chains are appended and the samples are returned as matrix of shape draws x params.

[devmotion]

If you specify append_chains = false, then instead a vector of matrices with the samples of each chain is returned.

[bgctw]

Thanks for this clarification and the option.