Julia Dictionaries and Sets

In the previous chapters, we learned aboutJulia ArraysandJulia Tuples。

Arrays are a type of collection. In addition, Julia has other types of collections, such as dictionaries and sets (unordered collection lists).

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Dictionary

A dictionary is a mutable container model that can store objects of any type.

Each key-value in the dictionarykey=>valuepair is separated by=>a colon, and each key-value pair is separated by a comma,and the entire dictionary is enclosed in curly braces{}as follows:

Create Dictionary

The syntax for creating a dictionary is as follows:

Dict("key1" => value1, "key2" => value2,,…, "keyn" => valuen)

The following example creates a simple dictionary, where key A corresponds to value 1, and key B corresponds to value 2:

Dict("A"=>1, "B"=>2)

Use a for loop to create a dictionary:

Key

Keys in a dictionary are unique. If we assign a value to an existing key, we do not create a new one, but modify the existing key.

Find a Key

We can use the haskey() function to check whether the dictionary contains the specified key:

You can also use thein()function to check whether the dictionary contains thekey/valuepair:

Add a Key/Value Pair

We can add a new key/value pair to an existing dictionary as follows:

Delete a Key/Value Pair

We can use thedelete!()function to delete a key from an existing dictionary:

Get All Keys in a Dictionary

We can use thekeys()function to get all keys in the dictionary:

Value

Each key in a dictionary has a corresponding value.

View All Values of a Dictionary

We can use thevalues()to view all values in the dictionary:

Dictionary as an Iterable

We can treat a dictionary as an iterable to view key/value pairs:

In the example,kvis a tuple containing each key/value pair.

Dictionary Sorting

Dictionaries are unordered, but we can use the sort() function to sort a dictionary:

We can use the SortedDict data type from the DataStructures.ji package to keep a dictionary always sorted.

To use the DataStructures package, you need to install it first. You can add SortedDict in the Pkg mode of the REPL using the add command.

In the REPL, enter the symbol]to enterpkgmode.

Syntax format for adding a package:

add 包名

After we add the DataStructures package below, the following examples can run normally:

(@v1.7) pkg> add DataStructures

For unregistered packages, you can directly specify a URL:

add https://github.com/fredrikekre/ImportMacros.jl

Local packages:

add 本地路径/包名.jl

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Set

A Julia Set is a collection of objects without duplicates; all elements are unique.

The following are the differences between a set and other types of collections:

• Elements in a set are unique
• The order of elements in a set is not important

Sets are used to create lists without duplicates.

Create a Set

With the Set constructor, we can create a set as follows:

Alternatively we can also use push!() function, as arrays, to add elements in sets as follows −

We can use thepush!()function to add set elements as follows:

We can use thein()function to check whether an element exists in the set:

Common Operations

Union, intersection, and difference are some common operations we can perform on sets. The functions corresponding to these operations areunion()、intersect()andsetdiff()。

Union

For two sets A and B, the set formed by combining all their elements is called the union of set A and set B.

Intersection

The intersection of sets A and B is the set containing all elements that belong to both A and B, and no other elements.

Difference

The difference of sets A and B is the set containing all elements that belong to A but not to B, that is, removing the elements that overlap between B and A.

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Examples of Common Functions for Dictionaries and Sets

In the following examples, functions commonly used in dictionaries are demonstrated, and they also apply to sets:

Create two dictionaries dict1 and dict2:

Dictionary union:

Dictionary difference:

Merge dictionaries:

Find the minimum value in the dictionary:

Other Extensions