On Mon, Feb 22 2016, Aleksandr Mikheev wrote:
> Hi everyone. I have two simple questions, answer to which I cannot find by
> myself.
>
> 1. Is there any way to add an element to array? For example, I have
> Array{...}(n,m) or Vector{...}(n). And I'd like to expand it, i.e. I want
> to have now Array{n+1,m} or Vector{...}(n+1). How can I do this?
See push! and resize! for vectors. For general arrays, I would just use
hcat to make a new one if I am only doing this a few times, but you can
find messages on the lists with tricks to avoid reallocation if
performance is critical (grow them by more than a single row, eg
doubling). Alternatively, you can use a vector of vectors and
concatenate them when you have the result.
> 2. Imagine I have an array [1 2 3 4 5 6 7 8 9 10; 12 4 5 0 2 0 45 8 0 7].
> Is there any easy way to remove all columns with 0 in second line?
> Something like filter!(...)?
Try something like
A[:,mapslices(col->all(col.!=0),A,1)]
This could be slightly faster (not benchmarked):
function columnswithzeros{T <: Number}(A::AbstractArray{T,2})
n,m = size(A)
z = zeros(Bool,m)
for col = 1:m
for row = 1:n
if A[row,col] == 0
z[col] = true
break
end
end
end
z
end
A[:,~columnswithzeros(A)]
Best,
Tamas
