Hi Often I would like to initialize an array without specifying an eltype in advance, even though I know all elements of the array will have the same concrete type. By way of example, function makesomearray() arr = [] for i in 1:10 element = some_computation(i) #some type stable co…

Or map: it also produces a collection with an element type that contains what actually goes in the array. For example: julia> a = [rand(Bool) ? rand(1:10) : randstring() for _ = 1:10] 10-element Vector{Any}: 9 "UUa9X3To" 6 "5NAPmkJw" 9 9 7 1 2 "aCmCF7vc" julia> map(length, a) 10-eleme…

if you know the type (not that you have to hard-code manually): T[] If you see an input array and like to have an empty array with same elements types: eltype(input_array)[] (also checkout useful functions like similar)

Thanks for your comment! However, those strategies do not work for the situation I have in mind. I am thinking of a scenario where there is no easy way to write down the type of element in advance, and the only practical way of knowing the type of element is via typeof(element). A example might be t…

then just use eltype or tyoepf. But mind in these cases, you can probably just push to Any[]. I don’t see a huge complicated Array of Struct being super performant anyways. (and you’re probably not using this array with such needs)

You have a good point that Array of complicated Struct might not be required for performance. You suggest to use eltype or typeof. Do you mind providing a code for doing it concisely? If I trye to use typeof(element) to initialize an empty array, , I need to first obtain element somehow, and the co…

It all depends on how your loop works. For example, I don’t see the point of repeatedly calling solve and push results somewhere. Notice, if you map(solve, array), the array probably will be typed

You could use a comprehension . Comprehensions determine the appropriate array type as elements are added.

@benninkrs @StefanKarpinski Thank you for your reply! I did not think of making a clever use of map for this purpose. That seems to work well if what I want is a single array. Sometimes, however, I’d like to create multiple arrays from a single for loop. I am trying to figure out what is the best i…

[image] tomohiro_soejima: It relies on StructArray . I am wondering if this is the best way to accomplish this Currently, use StructArray. The same widening strategy that collect uses in Base could be ported easily to functions returning a tuple and building up a tuple of arrays, but AFAIK s…

@tkf has implemented a couple of these things. There’s Empty in BangBang.jl, which is pretty much the idea you described, and InitialValues.jl for a more general idea.

A way to initialize an array without specifying its eltype in advance?

General Usage

mschauer September 28, 2020, 9:02am 12

Some relevant discussion towards the end of Skipping parts of a for loop in the first iteration

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A way to initialize an array without specifying its eltype in advance?

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