朱莉娅在矩阵中找到(行，列)而不是索引 [英] julia find in matrix with (row,col) instead of index

问题描述

在 Julia 中，您可以通过以下方式找到矩阵中元素的坐标:

In Julia you can find the coordinates of elements in a matrix via:

julia> find( x -> x == 2, [ 1 2 3; 2 3 4; 1 0 2] )
3-element Array{Int64,1}:
 2
 4
 9

这些值是正确的，但我更希望得到 (row,col) 元组.

These values are correct but I would prefer that I would get the (row,col) tuples instead.

(1,2)
(2,1)
(3,3) 

在 Julia 中实现这一目标的最简单方法是什么?

What is the easiest way to achieve this in Julia?

推荐答案

我不相信有内置的方法可以做到这一点，但这里有一个函数可以做到这一点

I don't believe there is an inbuilt way to do it, but here is a function to do it

function findmat(f, A::AbstractMatrix)
  m,n = size(A)
  out = (Int,Int)[]
  for i in 1:m, j in 1:n
    f(A[i,j]) && push!(out,(i,j))
  end
  out
end

例如

julia> findmat(x->x==2, [ 1 2 3; 2 3 4; 1 0 2] )
3-element Array{(Int64,Int64),1}:
 (1,2)
 (2,1)
 (3,3)

如果有大量的项目满足条件，那么分两次执行可能会更有效，但我对此表示怀疑.

If a large number of items satisfy the condition it might be more efficient to do it in two passes, but I doubt it.

对于较新版本的 Julia 替换

For newer versions of Julia replace

out = (Int,Int)[]

与

out = Tuple{Int, Int}[]

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