When you want to store and look up values based on a unique key, then the dictionary type Dict (also called hash, associative collection, or map in other languages) is what you need. It is basically a collection of two-element tuples of the form (key, value). To define a dictionary d1 as a literal value, the following syntax is used:

// code in Chapter 5\dicts.jl:
d1 = Dict(1 => 4.2, 2 => 5.3)

It returns Dict{Int64,Float64} with two entries: 2 => 5.3 and 1 => 4.2, so there are two key-value tuples here, (1, 4.2) and (2, 5.3); the key appears before the => symbol and the value appears after it, and the tuples are separated by commas.

To explicitly specify the types, use:

d1 = Dict{Int64,Float64}(1 => 4.2, 2 => 5.3)
If you use ...

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