Thanks! RaggedArrays.jl looks like a good start, though it looks
abandoned so I guess I’ll copy the necessary code (w/ License) and update as
needed.
> On 24 Feb 2016, at 5:25 PM, Tamas Papp <[email protected]> wrote:
>
> These are called "ragged arrays", searching the list for this term will
> show you attempts and issues, in particular
> https://github.com/JuliaLang/julia/issues/10064
> https://github.com/ReidAtcheson/RaggedArrays.jl
>
> For the moment you could just use a either
> a) a vector of vectors,
> b) a single vector which contains all vectors, and a vector of indexes
> that provides the positions.
>
> (a) is preferred when you want to grow the rows dynamically, or don't
> want to do too much programming. (b) is nice when the rows don't change,
> and/or you know something special about the structure (banded linear
> operators suggests this), or you want to pass it to routines which
> require this format (for example, this is the idiom for ragged arrays in
> Stan).
>
> Finally, if you want to use this matrix for linear algebra computations,
> look into the representation that those routines (eg in LAPACK) would
> use. If you do a lot of these operations and require conversion each
> time, it may not be worth it, then just go with the structure that is
> natively supported, maybe storing info on raggedness in a wrapper.
>
> Best,
>
> Tamas
>
> On Wed, Feb 24 2016, Sheehan Olver wrote:
>
>> I'm wondering if there's a natural data structure for a matrix whose rows
>> are of different length, in my case strictly growing. The usage is e.g.
>> representing coefficients in a 2D monomial expansion:
>>
>> f_00 + f_10 x + f_01 y + f_20 x^2 + f_11 xy + f_02 y^2 + …
>>
>>
>> So I want to do the following:
>>
>> F=TreeMatrix(Float64,1:n,n)
>>
>> F[1,1] # return f_00
>> F[1,2] # out of bounds error
>> F[1,1] # returns f_10
>> F[1,2] # returns f_01
>> F[1,3] # out of bounds error
>>
>>
>> It's easy to implement myself I suppose (probably more efficient to wrap a
>> Vector{Float64} than a Vector{Vector{Float64}}), but I was just curious if
>> such a thing exists.
>>
>> The next step on top of this is a data structure for banded linear
>> operators on trees.
>
