Julia :如何漂亮地打印数组？

Question

a= zeros(4,4)

像这样打印 a

> 4×4 Array{Float64,2}:
>  0.0  0.0  0.0  0.0
>  0.0  0.0  0.0  0.0
>  0.0  0.0  0.0  0.0
>  0.0  0.0  0.0  0.0

但是 println(a)像这样打印

[0.0 0.0 0.0 0.0; 0.0 0.0 0.0 0.0; 0.0 0.0 0.0 0.0; 0.0 0.0 0.0 0.0]

如何在函数中以以前的方式“打印” a？我希望出于调试目的。

Answer 1

让我在这里对这里发生的事情发表评论。您可以在docs中看到show(io, x)和show(io, mime, x)之间的关键区别:

help?> show(stdout, a)show([io::IO = stdout], x)

Write a text representation of a value x to the output stream io. New types Tshould overload show(io::IO, x::T). The representation used by show generallyincludes Julia-specific formatting and type information, and should beparseable Julia code when possible.

repr returns the output of show as a string.

To customize human-readable text output for objects of type T, defineshow(io::IO, ::MIME"text/plain", ::T) instead. Checking the :compact IOContextproperty of io in such methods is recommended, since some containers show theirelements by calling this method with :compact => true.

所以:

不带MIME的

show写入对象

的文本表示形式
带有MIME的

show尝试产生一种人类可读的格式。

现在，您可以在此处看到 print(io, x)退回到 show(io, x):

function print(io::IO, x)
    lock(io)
    try
        show(io, x)
    finally
        unlock(io)
    end
    return nothing
end

在REPL中，默认情况下， display会退回到 show(io, mime, a):

function display(d::REPLDisplay, mime::MIME"text/plain", x)
    io = outstream(d.repl)
    get(io, :color, false) && write(io, answer_color(d.repl))
    if isdefined(d.repl, :options) && isdefined(d.repl.options, :iocontext)
        # this can override the :limit property set initially
        io = foldl(IOContext, d.repl.options.iocontext,
                   init=IOContext(io, :limit => true, :module => Main))
    end
    show(io, mime, x)
    println(io)
    nothing
end

(在两种情况下，我都从Base复制了定义，最终您将使用默认的 print(a)和 display(a)操作-跳过过程中调用的方法)
您可以在Julia手册中找到有关 here的更多信息。
因此，就您的情况而言-正如Jun Tian所建议的，您可以使用 display。也只是为了表明这一切都归结为 show:

julia> a = zeros(4,4);

julia> show(stdout, a)
[0.0 0.0 0.0 0.0; 0.0 0.0 0.0 0.0; 0.0 0.0 0.0 0.0; 0.0 0.0 0.0 0.0]
julia> show(stdout, "text/plain", a)
4×4 Array{Float64,2}:
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0