How to display a sparse array on the REPL?

General Usage
,
1

If I construct a sparse matrix on the REPL, it can directly display the distribution of non-zero elements of the matrix:

julia> using SparseArrays

julia> sparse(round.(rand(5,5)))
5×5 SparseMatrixCSC{Float64, Int64} with 12 stored entries:
 1.0   ⋅   1.0   ⋅   1.0
  ⋅    ⋅    ⋅   1.0   ⋅
 1.0  1.0  1.0  1.0  1.0
  ⋅   1.0   ⋅   1.0   ⋅
  ⋅    ⋅    ⋅    ⋅   1.0

Now I want to construct a sparse matrix in a .jl script and display it when run the script, for example:

using SparseArrays
a = sparse(round.(rand(5,5)))
println("The sparse matrix is:")
# Print the non-zero elements' distribution on the REPL. How to write?
println("Over.")

How to write?

2

The REPL uses basically just uses the show method to display output. So you can just use show(x) in your script

3

The REPL calls display(a), which calls show(stdout, , "text/plain", a) (more precisely, it wraps stdout in an IOContext that limits output.

So, in your script you can either call display(a) or call show(io, "text/plain", a) if you want to output to a particular io stream.

1 Like
4

But this can’t display the figure:

using SparseArrays
a = sparse(round.(rand(5,5)))
println("The sparse matrix is:")
show(a)
println("Over.")

The sparse matrix is:
sparse([1, 2, 4, 5, 3, 4, 2, 3, 1, 2, 3, 4, 1], [1, 1, 1, 1, 2, 2, 3, 3, 4, 4, 4, 4, 5], [1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0], 5, 5)Over.
5

No, this is wrong. The 1-argument show(x) (which is also called by print(x) for most types) calls the 2-argument show(stdout, x). For matrices, this is less verbose than the 3-argument show(stdout, "text/plain", x) called by the REPL’s display.

Summary:

  • display(x) tells the current environment to display x in whatever way it thinks best. This might be a graphical display in something like a Jupyter notebook. By default (e.g. in scripts or in the text REPL), it calls show(io, "text/plain", x) or equivalently show(io, MIME"text/plain"(), x) for an appropriate io stream. (In the REPL, io is an IOContext wrapper around stdout.) The REPL uses display to output the result of an evaluated expression.
  • The 3-argument show(io, ::MIME"text/plain", x) method is verbose pretty-printing of x. By default (if no verbose method is defined for typeof(x)), it calls the 2-argument show(io, x).
  • The 2-argument show(io, x) is the default simple text representation of x. It is what is used by repr(x), and is typically the format you might use to input x into Julia. The 1-argument show(x) calls show(stdout, x).
  • print(x) calls print(stdout, x), which by default calls show(stdout, x). It mainly differs from show when x is a string, where print outputs the raw text but show outputs an escaped string enclosed in quotation marks.

Update May 2024: a version of this summary should be added to the manual (julia#54547).

3 Likes
6

Nice! Professional! Thanks a lot! :handshake: :handshake: