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similar

similar(array, [element_type=eltype(array)], [dims=size(array)])

Create an uninitialized mutable array with the given element type and size, based upon the given source array. The second and third arguments are both optional, defaulting to the given array's eltype and size. The dimensions may be specified either as a single tuple argument or as a series of integer arguments.

Custom AbstractArray subtypes may choose which specific array type is best-suited to return for the given element type and dimensionality. If they do not specialize this method, the default is an Array(element_type, dims...).

For example, similar(1:10, 1, 4) returns an uninitialized Array{Int,2} since ranges are neither mutable nor support 2 dimensions:

julia> similar(1:10, 1, 4)
1x4 Array{Int64,2}:
 4419743872  4374413872  4419743888  0

Conversely, similar(trues(10,10), 2) returns an uninitialized BitVector with two elements since BitArrays are both mutable and can support 1-dimensional arrays:

julia> similar(trues(10,10), 2)
2-element BitArray{1}:
 false
 false

Since BitArrays can only store elements of type Bool, however, if you request a different element type it will create a regular Array instead:

julia> similar(falses(10), Float64, 2, 4)
2x4 Array{Float64,2}:
 2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314
 2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314

Examples

julia> similar(1:10, 1, 4)
1x4 Array{Int64,2}:
 4419743872  4374413872  4419743888  0

julia> similar(trues(10,10), 2)
2-element BitArray{1}:
 false
 false

julia> similar(falses(10), Float64, 2, 4)
2x4 Array{Float64,2}:
 2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314
 2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314

In the above examples, similar is used to create uninitialized arrays with specific element types and dimensions based on the given source array.

1. Create an uninitialized array with specific element type and dimensions:

   julia> similar(1:10, 1, 4)
   1x4 Array{Int64,2}:
   4419743872  4374413872  4419743888  0

   This example creates a 1x4 uninitialized array of type Int64 based on the given range.

2. Create an uninitialized bit array with specific dimensionality:

   julia> similar(trues(10,10), 2)
   2-element BitArray{1}:
   false
   false

   Here, similar is used to create a 1-dimensional bit array with 2 elements based on the given trues(10,10) array.

3. Create an uninitialized array with a different element type:

   julia> similar(falses(10), Float64, 2, 4)
   2x4 Array{Float64,2}:
   2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314
   2.18425e-314  2.18425e-314  2.18425e-314  2.18425e-314

   This example creates a 2x4 uninitialized array of type Float64 based on the given falses(10) array.

Note: The specific array type returned by similar depends on the element type and dimensionality, and custom AbstractArray subtypes may specialize this method to provide appropriate array types.

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