Julia Notes Day2 -- string and collections

Char and String

A Char value represents a single character

c = 'x'
d = Int('x') # 120
e = Char(120)  # 'x'
f = '\u2200' # '∀': Unicode U+2200 (category Sm: Symbol, math)
g = 'A' + 1 # 'B'

String literals are delimited by double quotes or triple double quotes (not single quotes).

s = "\u2200 x \u2203 y" # "∀ x ∃ y"
s *= "世界" # "∀ x ∃ y世界"
length(s) # 9
sizeof(s) # 17
s[end] # '界': Unicode U+754C (category Lo: Letter, other)

findfirst('界',s) # 15

# Sequential iteration is implemented by the iterate function. 
# The general for loop:
for c in s
    print(c*' ')
end
# ∀   x   ∃   y 世 界

String literals are encoded using the UTF-8 encoding. UTF-8 is a variable-width encoding, meaning that not all characters are encoded in the same number of bytes ("code units"). In UTF-8, ASCII characters — i.e. those with code points less than 0x80 (128) – are encoded as they are in ASCII, using a single byte, while code points 0x80 and above are encoded using multiple bytes — up to four per character.

String indices in Julia refer to code units (= bytes for UTF-8), the fixed-width building blocks that are used to encode arbitrary characters (code points). This means that not every index into a String is necessarily a valid index for a character. If you index into a string at such an invalid byte index, an error is thrown

greet = "Hello"; whom = "world";

#Julia provides * for string concatenation
greet * ' ' * whom # "Hello world"

#interpolation into string literals using $
"$greet, $whom." # "Hello, world."

# triple-quoted strings are dedented to the level of the least-indented line.
str = """
           Hello,
           world.
         """
# "  Hello,\n  world.\n"

"1 + 2 = 3" == "1 + 2 = $(1 + 2)" # true

# repeat("A", 10)
'A'^10 # "AAAAAAAAAA"
"B"^10 # "BBBBBBBBBB"
"BA"^10 # "BABABABABABABABABABA"

Range and Vector

V = [i/2 for i in 1:10]

# Comprehensions can also be written without the enclosing square brackets, 
# producing an object known as a generator.
sum(1/n^2 for n=1:1000)

# convert a range to a vector by using the collect function.
vec = collect(1:2:7)
println(vec)  # Output: [1, 3, 5, 7]

Matrix

A = [1 2; 3 4] 
#= 2×2 Matrix{Int64}:
 1  2
 3  4
=#
B = A*A*A
#= 2×2 Matrix{Int64}:
 37   54
 81  118
=#
B == A^3 # true

C = A * 3
C == 3A  # true

sin.(A)
#= 2×2 Matrix{Float64}:
 0.841471   0.909297
 0.14112   -0.756802
=#

sin(A)
#= 2×2 Matrix{Float64}:
 -0.465581  -0.148424
 -0.222637  -0.688218
=#

A*[1,2]
#= 2-element Vector{Int64}:
  5
 11
=#

Dict

Dict("A"=>1, "B"=>2)
#= Dict{String, Int64} with 2 entries:
  "B" => 2
  "A" => 1
=#

List of functions of Collections

Base.iterate — Function

Base.IteratorSize — Type

Base.IteratorEltype — Type

Base.AbstractRange — Type

Base.OrdinalRange — Type

Base.AbstractUnitRange — Type

Base.StepRange — Type

Base.UnitRange — Type

Base.LinRange — Type

Base.isempty — Function

Base.empty! — Function

Base.length — Function

Base.checked_length — Function

Base.in — Function

Base.:∉ — Function

Base.eltype — Function

Base.indexin — Function

Base.unique — Function

Base.unique! — Function

Base.allunique — Function

Base.allequal — Function

Base.reduce — Method

Base.reduce — Method

Base.foldl — Method

Base.foldr — Method

Base.maximum — Function

Base.maximum! — Function

Base.minimum — Function

Base.minimum! — Function

Base.extrema — Function

Base.extrema! — Function

Base.argmax — Function

Base.argmin — Function

Base.findmax — Function

Base.findmin — Function

Base.findmax! — Function

Base.findmin! — Function

Base.sum — Function

Base.sum! — Function

Base.prod — Function

Base.prod! — Function

Base.any — Method

Base.any — Method

Base.any! — Function

Base.all — Method

Base.all — Method

Base.all! — Function

Base.count — Function

Base.foreach — Function

Base.map — Function

Base.map! — Function

Base.mapreduce — Method

Base.mapfoldl — Method

Base.mapfoldr — Method

Base.first — Function

Base.last — Function

Base.front — Function

Base.tail — Function

Base.step — Function

Base.collect — Method

Base.collect — Method

Base.filter — Function

Base.filter! — Function

Base.replace — Method

Base.replace — Method

Base.replace! — Function

Base.rest — Function

Base.split_rest — Function

Base.getindex — Function

Base.setindex! — Function

Base.firstindex — Function

Base.lastindex — Function

Base.AbstractDict — Type

Base.Dict — Type

Base.IdDict — Type

Base.WeakKeyDict — Type

Base.ImmutableDict — Type

Base.haskey — Function

Base.get — Function

Base.get! — Function

Base.getkey — Function

Base.delete! — Function

Base.pop! — Method

Base.keys — Function

Base.values — Function

Base.pairs — Function

Base.merge — Function

Base.mergewith — Function

Base.merge! — Function

Base.mergewith! — Function

Base.sizehint! — Function

Base.keytype — Function

Base.valtype — Function

Base.AbstractSet — Type

Base.Set — Type

Base.BitSet — Type

Base.union — Function

Base.union! — Function

Base.intersect — Function

Base.setdiff — Function

Base.setdiff! — Function

Base.symdiff — Function

Base.symdiff! — Function

Base.intersect! — Function

Base.issubset — Function

Base.:⊈ — Function

Base.:⊊ — Function

Base.issetequal — Function

Base.isdisjoint — Function

Base.push! — Function

Base.pop! — Function

Base.popat! — Function

Base.pushfirst! — Function

Base.popfirst! — Function

Base.insert! — Function

Base.deleteat! — Function

Base.keepat! — Function

Base.splice! — Function

Base.resize! — Function

Base.append! — Function

Base.prepend! — Function

Core.Pair — Type

Base.Pairs — Type

Julia Notes Day2 -- string and collections

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