matrixjulianegate

How to apply not operator to all matrix elements in Julia?

I need to apply "not" operator to matrix of zeros and ones in Julia. In Matlab I would do this:

A=not(B);

In Julia I tried doing this:

A = .~ B;

and

A = .! B;

It should turn zeros to ones and ones to zeros but I get error as a result or all matrix elements are some negative numbers that I didn't enter. Thanks in advance!

Solution

  • The issue with A = .!B is that logical negation, !(::Int64), isn't defined for integers. This makes sense: What should, say, !3 reasonably give?

    Since you want to perform a logical operation, is there a deeper reason why you are working with integers to begin with?

    You could perhaps work with a BitArray instead which is vastly more efficient and should behave like a regular Array in most operations.

    You can easily convert your integer matrix to a BitArray. Afterwards, applying a logical not works as expected.

    julia> A = rand(0:1, 5,5)
5×5 Array{Int64,2}:
 0  0  0  1  1
 0  1  0  0  1
 0  1  1  1  0
 1  1  0  0  0
 1  1  1  0  0

julia> B = BitArray(A)
5×5 BitArray{2}:
 0  0  0  1  1
 0  1  0  0  1
 0  1  1  1  0
 1  1  0  0  0
 1  1  1  0  0

julia> .!B
5×5 BitArray{2}:
 1  1  1  0  0
 1  0  1  1  0
 1  0  0  0  1
 0  0  1  1  1
 0  0  0  1  1

    The crucial part here is that the element type (eltype) of a BitArray is Bool, for which negation is obviously well defined. In this sense, you could also use B = Bool.(A) to convert all the elements to booleans.