[ViralBShah]

A range view of a sparse vector, view(x, 2:6), is converted to a SparseVector by reading it as a dense vector, so SparseVector, sparse, sparsevec, convert and sparse vcat, hcat and hvcat take O(n), drop stored zeros and give Int indices, and kron of a range view is dense.

using SparseArrays
x = sparsevec(Int32[2, 4, 5], [1.0, 0.0, 3.0], 7); v = view(x, 2:6)

Before

SparseVector(v) = sparsevec([1, 4], [1.0, 3.0], 5)
vcat(v, v) = sparsevec([1, 4, 6, 9], [1.0, 3.0, 1.0, 3.0], 10)
typeof(kron(v, x)) = Vector{Float64}

After

SparseVector(v) = sparsevec(Int32[1, 3, 4], [1.0, 0.0, 3.0], 5)
vcat(v, v) = sparsevec(Int32[1, 3, 4, 6, 8, 9], [1.0, 0.0, 3.0, 1.0, 0.0, 3.0], 10)
typeof(kron(v, x)) = SparseVector{Float64, Int32}

For w = view(sparsevec([1, n], [1.0, 2.0], n), 1:n) with n = 10^7 and y = sparsevec([1], [1.0], 2), the minimum of three runs and the @allocated of a warm call:

f(w)	main	branch
SparseVector(w)	0.030 s, 19.1 MiB	2.3e-7 s, 240 B
vcat(w, w)	0.056 s, 38.2 MiB	3.8e-7 s, 1.1 KiB
kron(w, y)	0.067 s, 152.6 MiB	3.8e-7 s, 976 B

The SparseVector copy constructors and sparsevec, which #1119 widened to whole views, also take SparseVectorPartialView, whose nonzeroinds and nonzeros give its stored entries relative to the range. convert and the concatenations reach them through _makesparse. kron takes range views in _SparseKronGroup and in its vector methods, so they go through the same conversion. The _sparsevector helper that sparse map uses for views now calls SparseVector instead of repeating it.

This touches dispatch.

Potential breakage: for a range view, these conversions and concatenations keep its stored zeros and the parent's index type, and kron of one is sparse rather than dense, as for x[2:6].

Products with a range view are in #1135.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.69%. Comparing base (61f75e0) to head (eebacf8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1134   +/-   ##
=======================================
  Coverage   94.68%   94.69%           
=======================================
  Files          16       16           
  Lines       10433    10434    +1     
=======================================
+ Hits         9879     9880    +1     
  Misses        554      554           

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