[ViralBShah]

mapreduce(pred, |, A; dims=1, init) and mapreduce(pred, &, A; dims=1, init) on a sparse matrix ignore init: the result is the reduction of each column alone, where dense folds it into the initial value.

Before

julia> A = sparse([1.0 2.0; 0.0 3.0]);

julia> mapreduce(x -> x > 5, |, A; dims=1, init=true)
1×2 Matrix{Bool}:
 0  0

julia> mapreduce(!iszero, &, A; dims=1, init=false)
1×2 Matrix{Bool}:
 0  1

After

julia> mapreduce(x -> x > 5, |, A; dims=1, init=true)
1×2 Matrix{Bool}:
 1  1

julia> mapreduce(!iszero, &, A; dims=1, init=false)
1×2 Matrix{Bool}:
 0  0

The short-circuiting _mapreducerows! kernel for | and & assigned each column's reduction to R[1, ii], which on entry holds the initial value. It now reads that value first, skips a column the initial value already decides, and stores the column's reduction otherwise. The & method reuses the | kernel with the negated predicate as before, but passes a negate::Bool flag in place of the post function, so that the kernel can also interpret the initial value.

mapreduce(>(2.0), |, A; dims=1) on a 10^4 × 10^3 matrix with 10^6 stored entries, none of which satisfies the predicate, takes 273 μs and 1280 bytes before and 274 μs and 1280 bytes after.

Split from #1022.

This is a wrong result on released versions too (Julia 1.13 gives the same output), so it is a backport candidate.

Written by Claude Code.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.78%. Comparing base (c0f75f0) to head (23e1ae6).
⚠️ Report is 35 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1069      +/-   ##
==========================================
+ Coverage   94.75%   94.78%   +0.02%     
==========================================
  Files          16       16              
  Lines        9885     9880       -5     
==========================================
- Hits         9367     9365       -2     
+ Misses        518      515       -3     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ViralBShah]

Reviewed by Codex at 23e1ae6.

No actionable findings. The initial-value short circuit and the negated-predicate path handle | and & consistently, including columns with implicit zeros and fully stored columns.