Boolean operations on arrays?

[Daniel Carrera]

Hello,

I have two boolean arrays and I am trying to obtain the boolean array resulting from a component-wise `AND`:

julia> [true, true, false] .&& [false, true, true]

ERROR: syntax: invalid identifier name "&&"

julia> [true, true, false] .& [false, true, true]

ERROR: type Array has no field &

Can anyone figure out what I'm doing wrong? I was hoping that `.&` and `.&&` would apply the operation on a per-component basis. Help?

Cheers,

Daniel.

[Yichao Yu]

julia> [true, true, false] & [false, true, true]
3-element Array{Bool,1}:
false
true
false



>
> Cheers,
> Daniel.

[Daniel Carrera]

It looks like I can get the right effect using component-wise multiplication:

julia> ![true, true, false] .* [false, true, true]

3-element Array{Bool,1}:

 false

 false

  true

Is this the correct solution or is this an ugly hack?

Cheers,

Daniel.

[Matt Bauman]

The bitwise operations (&, |) broadcast over arrays and work just fine for this.  Watch out for their precedence, though: you need to wrap them in parentheses if you want to combine them with the result of comparisons `(A == 1) | (A == 2)`.

[Seth]

Note that the broadcasting works for sparse matrices only on recent builds.

[Daniel Carrera]

On Monday, 21 September 2015 14:39:13 UTC+2, Yichao Yu wrote:

julia> [true, true, false] & [false, true, true]
3-element Array{Bool,1}:
false
 true
false 

Thanks! What is the difference between & and && ? 

[Sisyphuss]

& works for array

&& works for scale

[Matt Bauman]

More concretely, && and || are control flow operators.  They short circuit.  Therefore, they require Boolean arguments and aren't real functions.  They're syntax.

& and | are bitwise operations and real, extendable functions.  They can operate on booleans *and* integers, performing bitwise arithmetic (often used for bit flags):

julia> 0x2345 & 0x0F0F

0x0305

julia> ans | 0x6070

0x6375

[Daniel Carrera]

Oh.... Thanks!