I want to plot a sparse matrix as a heatmap, something like this: julia> using Plots, SparseArrays julia> x = sprand(Float64, 5, 5, 0.5) 5×5 SparseMatrixCSC{Float64, Int64} with 11 stored entries: ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ 0.838339 0.330949 ⋅ ⋅ ⋅ …

[image] lmiq: Can anyone see a smart way of achieving this without creating a dense matrix as an intermediate? Is there a strong reason to avoid this? The memory usage for heatmap is probably going to be proportional to the size of a dense matrix anyway. To ensure that you only avoid plotti…

Plots.spy seems to not allocate, although its a bit difficult to confirm because @edit spy(x) does not really lead to anywhere useful. julia> using BenchmarkTools, Plots, SparseArrays julia> x = sprand(Float64, 500, 500, 0.01) julia> @benchmark Plots.spy(x) BenchmarkTools.Trial: 10000 samples with…

Yes, probably. For the moment I added a safeguard to just avoid plotting. But I think that “heatmap” using a memory proportional to the size of the dense matrix is an implementation detail. For instance, a scatter plot can easily look pretty much the same and use only the actual values for plotting. …

Uhm, I didn’t know about spy. That seems a reasonable alternative, if tuned. Thanks!

Skip empty entries of sparse matrix when plotting a heatmap

General Usage

lmiq January 30, 2026, 8:11pm 6

I actually ended using a scatter plot, which I found also allows creating a colorbar for the marker colors. That worked fine.

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Skip empty entries of sparse matrix when plotting a heatmap

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