In your example y is a row matrix, rather than a vector. If you make it a
vector it works:
julia> a = [-1 2
3 -4]
2x2 Array{Int64,2}:
-1 2
3 -4
julia> y = [1, 2]
2-element Array{Int64,1}:
1
2
julia> a[:,y]
2x2 Array{Int64,2}:
-1 2
3 -4
This seems like it may not be what you want though. Can you explain what
you'd like it to do?
On Sat, Dec 19, 2015 at 7:44 PM, Lex <[email protected]> wrote:
> I am expecting [-1 -4] in the Julia example.
>
>
> On Saturday, December 19, 2015 at 4:42:07 PM UTC-8, Lex wrote:
>>
>> Hi
>>
>> In Python, I am able to select values like this:
>>
>> >>> a = np.matrix([[-1,2],[3,-4]])
>> >>> y = np.matrix([1,0])
>> >>> a[range(2),y]
>> matrix([[2, 3]])
>> >>>
>>
>> Is there any equivalent in Julia or using a loop is the only way?
>>
>> julia> a
>> 2x2 Array{Int64,2}:
>> -1 2
>> 3 -4
>>
>> julia> y
>> 1x2 Array{Int64,2}:
>> 1 2
>>
>> julia> a[:, y]
>> ERROR: MethodError: `index_shape_dim` has no method matching
>> index_shape_dim(::Array{Int64,2}, ::Int64, ::Array{Int64,2})
>>
>> You might have used a 2d row vector where a 1d column vector was required.
>> Note the difference between 1d column vector [1,2,3] and 2d row vector [1
>> 2 3].
>> You can convert to a column vector with the vec() function.
>> Closest candidates are:
>> index_shape_dim(::Any, ::Any, ::Real...)
>> index_shape_dim(::Any, ::Any, ::Colon)
>> index_shape_dim(::Any, ::Any, ::Colon, ::Any, ::Any...)
>> ...
>> in getindex at abstractarray.jl:488
>>
>> julia> a[:, y[]]
>> 2-element Array{Int64,1}:
>> -1
>> 3
>>
>> julia> a[:, y[:]]
>> 2x2 Array{Int64,2}:
>> -1 2
>> 3 -4
>>
>> julia>
>>
>>
>>
