Fast and simple search for an object by field value, like in a database

New to Julia
1

Hello, I need a fast and simple search for an object by field value, like in a database.

for example,
search for an object with the maximum field value,
search by object field value
search object with next value up

What data structure can i use for this?

May be i should create a list or dict for searching fields?

2

Put your objects in a array and use findfirst, findmax etc. If you need better than O(n), you’ll something else, such as a tree.

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3

Databases are fast because they index various columns then can use those index to find the correct row (object) in the database quickly. I haven’t really run into any package that maintains multiple indexes on a set of objects so you can quickly find the object you want based on some criteria.

You could probably create a custom object using the structures in:

Something like:

using DataStructures

struct Foo
    value1::Int64
    value2::Float64
end

struct Collection
    data::Vector{Foo}
    lookup1::SortedDict{Int64, Int}
    lookup2::SortedDict{Float64, Int}
end

function Base.push!(c::Collection, v::Foo)
    if haskey(c.lookup1, v.value1) || haskey(c.lookup2, v.value2)
        throw("Foo is not unique")
    end
    push!(c.data, v)
    c.lookup1[v.value1] = length(c.data)
    c.lookup2[v.value2] = length(c.data)
end

function highest_value1(c::Collection)
    return c.data[last(c.lookup1)]
end

function lowest_value1(c::Collection)
    return c.data[first(c.lookup1)]
end

You would have to take a look at the documentation of Datastructures.jl it gives you methods to iterate over the SortedDict objects in key order.

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