On Saturday, June 4, 2016 at 8:19:02 AM UTC-4, Christopher Fisher wrote:
>
> I was wondering if someone would be willing to help me with creating
> user-defined types. I've been using Julia for about two years now but I am
> new to the idea of creating custom types. I'm trying to create a population
> of agents/individuals in a simple epidemiological simulation. I would like
> the population of individuals to be structured as a 2 dimensional array
> with rows as individuals and columns as properties. This would be somewhat
> similar to a DataFrame, but potentially more flexible. I want to be able to
> index an individual like so: population[1]. This woud list all of the
> information for individual 1. I would also like to be able to look at an
> attribute across individuals: population.infected or population[:infected].
> At the same time, I would like to have to flexibility of using an array to
> keep track of individuals: typeof(population.history[1]) is Array{Int64,1}.
> Based on existing documentation and examples, I have only been able to
> create individuals but cannot figure out how to create a population as
> described above:
>
> type Person
> infected::Int64
> vaccinated::Int64
> dead::Int64
> history::Array{Int64,1}
> end
>
It sounds like you just want an array of your Person type.
e.g.
population = Person[] # create an empty population
push!(population, Person(0, 2, 0, Int64[3,4,5])) # add a person to the
population
population[1].dead # access the "dead" field of the first person in the
population
population[1].history[3] # access history[3] from person 1
Of course, you can make working with the Person type a lot nicer by
defining more methods. e.g. you probably want to have a "show" method to
pretty-print a person, for example:
Base.show(io::IO, p::Person) = print(io, "Person(infected=", p.infected, ",
vaccinated=", p.vaccinated, ", dead=", p.dead, ", history=", p.history)
When designing your types, you also want to think carefully about your
fields. e.g. aren't infected, dead, etc. really Boolean fields? If you
can encode "history" into a fixed-width field (e.g. a single 64-bit
integer), it will be much more efficient. And arrays of persons will be
more efficient if you can make the person immutable --- you only need a
(mutable) type if you need to have multiple references to the same
individual, where modifying one reference's fields will change the data
seen from all the references.
