Thanks for your suggestions Steven. You are correct. I could many of those
fields as Boolean and maybe there is a reason to prefer that rather than
using 1 and 0s.
Initially, I also tried to push the individuals into an empty array as you
suggested. This worked well, except I was not able to query across
individuals:
type Person
infected::Int64
vaccinated::Int64
dead::Int64
history::Array{Int64,1}
end
population = Person[] # create an empty population
push!(population, Person(0, 2, 0, Int64[3,4,5])) # add a person to the
population
push!(population, Person(0, 2, 0, Int64[3,4,5]))
population.infected
LoadError: type Array has no field infected
while loading In[16], in expression starting on line 10
What I was hoping is that it would list the infection status for all
members of the population. Is there any way to do that?
On Saturday, June 4, 2016 at 10:47:55 AM UTC-4, Steven G. Johnson wrote:
>
>
>
> 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.
>
