I am playing around with a custom named array and trying to figure out how to make it play nicely with custom indices, such as those in @mbauman ’s fantastic InvertedIndices package. Here’s a toy example, simple as I could make it: # A struct representing a named index struct Name{T} name::T en…

Yeah, it’s hard to design interfaces that simultaneously allow for dispatch on either array or index without ambiguity. The to_indices method table is geared towards dispatch on the leading index type. As such, I’d define: Base.to_indices(A, inds, I::Tuple{Name, Vararg{Any}}) = to_indices(A, …

That comment was about what an array returns from axes — which is still true. But you can use any custom type as an index so long as your getindex method supports it. You must also support integer indices, though, so typically this means that you can lean on to_indices to convert your esoteric non…

Thanks, this helped a lot. Is this documented? I could not find it in the custom indexes devdocs . Also, suppose (for a toy problem) that I have a 2-dimensional matrix, and I want to allow indexing with names in the second axis. How would I write to_indices so that it resolves n[1:2, [:a, :b]] and s…

Very enlightening, thanks! My use case is also more complicated — like AxisArrays, I want to allow different names for different dimensions. And I’d like to allow pretty much anything (other than possibly Colon and CartesianIndex) as an index — is there a way to write the specialized non-ambiguous …

See the to_indices documentation for some of this. That custom indexing devdocs isn’t really about this case — it’s about offset arrays. Yes, I intentionally punted on the harder task of different names in different dimensions. You can figure out which dimension you’re on based upon the number of …

Ah, clever! I think that’s the missing piece.

The key thing to remember about extending most any method (particularly complicated ones) is that you want to look at what already exists to figure out how you’ll plug in. Here are the three-argument methods that exist in Base for to_indices: # 7 methods for generic function "to_indices": [1] to_i…

It works! using InvertedIndices struct Name{T} name::T end struct Arr{T, N} <: AbstractArray{T, N} data::Array{T, N} name_to_index::Tuple names::Tuple function Arr(data::AbstractArray{T, N}, names) where {T, N} name_to_index = Tuple(Dict(ks .=> vs) for (ks, vs) in (zip…

Custom indexing for a named array

General Usage

Tamas_Papp January 24, 2019, 7:26am 3

From an earlier discussion, I was under the impression that only integer custom indexes are supported by the interface, did that change?

Topic		Replies	Views
How to use custom indices General Usage indexing	4	3935	March 20, 2018
Making type stable code Performance	6	1173	March 12, 2018
Looking for the right structure General Usage question	1	559	March 28, 2018
N-dim dict General Usage question	4	329	August 11, 2021
Writing `broadcast_c` for struct with custom indexing General Usage	7	853	December 12, 2018

Custom indexing for a named array

Related topics