A,
There are a number of ways to do this, and the examples are just based on
what you suggested as an array of structs.
The array of uninitialized structs would be roughly equivalent to the C
version of allocating an array of pointers to structs of ExampleEvent
(without allocating the struct itself). The struct is uninitialized -- so
you can't set a value of a named field until it's allocated.
As far as I see it, this is just a syntax issue, as the concept is the same
in Julia and C.
One simple solution to continue on this example would be to define a
function to give you the event you care about (by index) that includes
initialization. You can then process events for fields as you see fit and
out of order.
julia> function get_event(v::Vector{ExampleEvent}, i)
n = length(v)
if i > n
for j in n:i
push!(v, ExampleEvent("",0,0,0,0,0,0)) # default values
end
end
v[i]
end
Then you can initialize a zero length vector and use it as such:
julia> events = Vector{ExampleEvent}()
0-element Array{ExampleEvent,1}
julia> e = get_event(events, 3); e.fld1 = "asdf"; e.fld3 = 3; e.fld7 = 7;
events
4-element Array{ExampleEvent,1}:
ExampleEvent("",0,0,0,0,0,0)
ExampleEvent("",0,0,0,0,0,0)
ExampleEvent("asdf",0,3,0,0,0,7)
ExampleEvent("",0,0,0,0,0,0)
Perhaps that helps.
Cameron
On Fri, Jul 22, 2016 at 2:38 PM, <[email protected]> wrote:
>
> Thanks Cameron.
>
> What I wanted to do was assign values to fields but the example you posted
> requires me to pass values to all fields in my type.
>
> If I do: events[1] = ExampleEvent("asdf",123), julia throws an error since
> I need to pass values to ALL my type's fields. I don't always have to use
> all fields & sometimes do not have data for all fields, thus I don't want
> to be obligated to pass even null values to them since it is
> verbose/excessive. Nor do I want to rewrite constructors for all fields
> since I already have named fields for sake of programming ease.
>
> See what I mean?
>
> Moreover, let's say I've filled 10 elements of my 1000 element array & a
> few milliseconds later I get a value for element 5, fld3. How do I index
> into element 5 of the events Vector & ONLY set fld3?
>
> Yes I've seen push! & looks good but I'm pretty religious about
> precallocating in any lang even if it is much larger than needed since
> processing these datasets require as much efficiency as possible.
>
> I think more intuitive Composite Type Arrays for morons like me would make
> Juila much easier to work with since I've seen a fair amount of
> uncertainty/confusion from people having similar conceptual use cases. I
> know I'm thinking from a perspective of other language(s) but some language
> constructs are there because they work & make a programmer's life easier.
> Is there an easy way to set field value(s) whenever I get them?
>
> On Friday, July 22, 2016 at 2:01:41 PM UTC-4, Cameron McBride wrote:
>>
>> Your ExampleEvent is completely analagous to a C-like struct. With
>> Stefan's bit, you now have a single dimension array of ExampleEvent type
>> (hence ndims(events) is 1).
>>
>> You can do this:
>> julia> events[1] = ExampleEvent("asdf",2,3,4,5,6,7)
>> ExampleEvent("asdf",2,3,4,5,6,7)
>>
>> And if you have more, you can do this:
>> julia> push!(events, ExampleEvent("ghjk", 2,3,4,5,6,7))
>> 1001-element Array{ExampleEvent,1}:
>> ExampleEvent("asdf",2,3,4,5,6,7)
>> #undef
>> ⋮
>> #undef
>> ExampleEvent("ghjk",2,3,4,5,6,7)
>>
>> Cameron
>>
>> On Fri, Jul 22, 2016 at 1:48 PM, <[email protected]> wrote:
>>
>>> Thanks Stefan!
>>>
>>> I thought it would be like declaring a struct array in c/c++ i.e.
>>> something like ExampleEvent events[2][1000]; Then set each field in the
>>> events array as I encounter the required value in my algo: e.g.
>>> events[1][1].fld1 = "ABC"; events[1][1].fld2 = 123; etc
>>>
>>> How do I access elements in the events Vector since ndims(events) = 1? I
>>> don't see anything in the docs about indexing into a preallocated Vector
>>> data structure. I see methods like push! splice! etc but not anything that
>>> will let me use the elements of my preallocation on the fly.
>>>
>>>
>>> On Thursday, July 21, 2016 at 3:21:54 PM UTC-4, Stefan Karpinski wrote:
>>>>
>>>> It's a little unclear what you want to do that you can't figure out how
>>>> to accomplish. You can allocate an uninitialized vector of ExampleEvent
>>>> objects:
>>>>
>>>> julia> type ExampleEvent
>>>> fld1::ASCIIString
>>>> fld2::Int16
>>>> fld3::Int64
>>>> fld4::Int64
>>>> fld5::Int64
>>>> fld6::Int64
>>>> fld7::Int64
>>>> end
>>>>
>>>> julia> events = Vector{ExampleEvent}(1000)
>>>> 1000-element Array{ExampleEvent,1}:
>>>> #undef
>>>> #undef
>>>> #undef
>>>> ⋮
>>>> #undef
>>>> #undef
>>>> #undef
>>>>
>>>>
>>>>
>>>>
>>>> On Thu, Jul 21, 2016 at 2:51 PM, <[email protected]> wrote:
>>>>
>>>>>
>>>>> Hi
>>>>>
>>>>> I was working on processing large data sets & historically I've used
>>>>> structs in C++ & other languages for this type of task. I attempted to use
>>>>> a Composite Type in Julia & preallocate a large array before filling it
>>>>> w/values as my algo processes the data.
>>>>>
>>>>> My example was:
>>>>>
>>>>> type ExampleEvent
>>>>>
>>>>> fld1::ASCIIString
>>>>> fld2::Int16
>>>>> fld3::Int64
>>>>> fld4::Int64
>>>>> fld5::Int64
>>>>> fld6::Int64
>>>>> fld7::Int64
>>>>>
>>>>> end
>>>>>
>>>>> I googled around & from what I found, & all the docs examples I tried
>>>>> out, there isn't an obvious way to declare an array of composite type
>>>>> without having to do some work arounds.
>>>>>
>>>>> I liked the language in several other respects but it seems to be
>>>>> missing helpful tools to make the programmer's life easy. Am I missing
>>>>> something? If not, why is a data structure like this not easily available?
>>>>>
>>>>> thanks in advance
>>>>>
>>>>> best,
>>>>> A
>>>>>
>>>>
>>>>
>>
