I have a row vector ‘a’ with a given coordinate (x, y, z) and I need to obtain the row in a coordinates array (B) with the coordinates are closest to the row vector ‘a’. I’ve been using a function that I found on the web:

You’ve written a[j] == B[i,j] for the comparison, but == is just a function that returns true/false, and you just need to put isapprox in its place. There’s a built-in infix isapprox operator ≈ which uses default tolerances, and if rtol=sqrt(eps), atol=0 suffices for your purposes, you could write a[j] ≈ B[i,j]. Otherwise, replace the comparison with isapprox(a[j], B[i,j], atol=???, rtol=???).

Thus, may I suggest to use something (for me) much more clear and efficient like an explicit loop e.g.

function matchrow(a, B::AbstractMatrix; kw...)
r = 1
while r ≤ size(B, 1)
c = 1
while c ≤ size(B, 2) && isapprox(a, B[r, c], kw...)
c += 1
end
c > size(B, 2) && return r
r += 1
end
return nothing
end