Printing zero elements in lines of a sparse matrix

General Usage
1

Dear all,
I would like to print the non-zero elements along a give line of a sparse matrix.
In fact I’m trying to find a way to reproduce the behaviour of MATLAB. For example, here’s how a line is printed in MATLAB, it’s very useful:
image
So far, I’ve tried a similar approach with Julia but it seems that it converts the row to a dense row (hence full of zeros) before printing it. Any hint regarding printing sparse matrix elements?
Cheers!

2

IIUC this is pretty much the normal behaviour in Julia:

julia> using SparseArrays

julia> sp = sprand(10,10,0.1)
10×10 SparseMatrixCSC{Float64, Int64} with 11 stored entries:
  ⋅    ⋅    ⋅   0.27207    ⋅    ⋅    ⋅         ⋅         ⋅          ⋅ 
  ⋅    ⋅    ⋅    ⋅         ⋅    ⋅    ⋅         ⋅         ⋅          ⋅ 
  ⋅    ⋅    ⋅    ⋅         ⋅    ⋅    ⋅         ⋅         ⋅          ⋅ 
  ⋅    ⋅    ⋅    ⋅         ⋅    ⋅    ⋅         ⋅         ⋅          ⋅ 
  ⋅    ⋅    ⋅    ⋅         ⋅    ⋅    ⋅         ⋅        0.0865405  0.9079
  ⋅    ⋅    ⋅   0.246534   ⋅    ⋅   0.743724  0.611045   ⋅          ⋅ 
  ⋅    ⋅    ⋅    ⋅         ⋅    ⋅    ⋅         ⋅        0.684832    ⋅ 
  ⋅    ⋅    ⋅   0.626594   ⋅    ⋅    ⋅         ⋅         ⋅          ⋅ 
  ⋅    ⋅    ⋅   0.541967   ⋅    ⋅    ⋅         ⋅         ⋅          ⋅ 
  ⋅    ⋅    ⋅    ⋅         ⋅    ⋅    ⋅         ⋅        0.330361   0.940725

julia> sp[:,4]
10-element SparseVector{Float64, Int64} with 4 stored entries:
  [1 ]  =  0.27207
  [6 ]  =  0.246534
  [8 ]  =  0.626594
  [9 ]  =  0.541967
3

Hmmm OK, thanks!
I confirm I get the same result than you from execution within the REPL.
In my case I was running within a script:

 println(typeof(Kuusc))
 println(Kuusc[45,:])

and what comes out is:

image
image1460×206 6.67 KB
and so on
Same with @show.
Maybe, this is because I’m doing this in the middle of a script and not from the REPL directly (and in MATLAB I’m running in the debugger…).

4

See pretty-printing in Julia — println uses show(io, x), but the REPL display uses show(io, "text/plain", x). So do e.g.

show(stdout, "text/plain", Kuusc[45,:])

PS. Please use quoted text, not screenshots.

3 Likes
5

Thanks a lot, I had no clue about this difference in printing style.
I have tried your suggestion: the printing is indeed different but still not similar to REPL. Here’s what comes out:

840-element view(::SparseMatrixCSC{Float64, Int64}, 43, :) with eltype Float64:
 0.0
 0.0
 0.0
 0.0
 0.0
 0.0
 0.0

I’ve truncated it because it does print all elements of the sparse matrix. Sorry for the screenshots, I’ve partly edited my post above.

6

Did you use views function in the print or show function? If not, why the type of output is a view?

7

Thanks for point ting this out. I understood why this was a view. My main function was decorated with the @views macro.
Now, I’ve removed it and the printing suggested by @stevengj works perfectly!
Thanks a lot to all of you!