vector
Create
Julia的vector与R和Python中的list类似，vector中可以放入任何东西。
v1 = [2, 3, 5, "Math", 11, 13, 17]
length(v1) #7
1:2:7 #step = 2
range(start=1,stop=10,length=10) #1.0:1.0:10.0
collect("APPLE") == ['A','P','P','L','E'] # string to vector # Vector{Char}
collect((1,3,5)) == [1,3,5]# tuple to vector # Vector{Int64}
其实Julia中的vector只是一维的array，用typeof便能看出来。
typeof([1,3,5])
# Vector{Int64} (alias for Array{Int64, 1})
初始化
zeros(3) == [0.0,0.0,0.0]
zeros(Int64,3) == [0,0,0]
y=Vector{Float64}(undef, 3) #3元素，元素值未初始化
fill!(y, 100) #填充3个位置
collect(1:5) == [1,2,3,4,5] # range to vector
python中也叫列表推导式
[x*x for x in 1:10 if x % 3 == 1]
遍历
# --------------------- eachindex ---------------------
v1 = [1, 3, 4, 9, 13]
for x in eachindex(v1)
println("v1[", x, "] = ", v1[x])
end
# --------------------- = ---------------------
for i = 1:length(v1)
println("v1[", i, "] = ", v1[i])
end
# --------------------- in ---------------------
for x in v1
println(x)
end
# --------------------- enumerate --------------------
for (i, xi) in enumerate(v1)
println("v1[", i, "] = ", xi)
end # 同时对向量下标和元素值遍历
Retrieve
v1[1]
v1[end] # 相当于python中的 v1[-1]
# ---------------------用数组作为下标---------------------
v1[2:4]
v1[:]
v1[2]=0 # 原地修改
# ---------------------用条件作为下标 布尔索引---------------------
v1 = [2, 3, 5, 7, 11, 13, 17]
b = v1 .<= 10
v1[b] == v1[v1 .<= 10]
type
v1 = [1.2, 2, 3.6]
eltype(v1) # 元素类型
typeof(v1) # 容器类型
v1[2] = "abc" # 报错 因为v1是Int64类型
成员判断
8 in 1:8 # true
[3,5] .∈ Ref([1,2,3]) # return 1 0
a=[1,3,5,3]; b=[1,2,3]
indexin(a, b) # 返回向量a的每个元素首次出现在b中的位置， 没有时返回nothing
allunique([1,2,3,3]) # 判断是否元素彼此不同
Delete
pop!(a) # 删除a的最后一个元素
popfirst!(a) # 删除a的第一个元素
splice!(a, [2,3]) # 删除2，3位置上的元素
deleteat!(a, [2,3]) # 无返回值
empty!(a) #清空
Update
# ---------------------增-------------------
push!(a, 2) # 将2添加到向量a的末尾
pushfirst!(a, 2) # 将2添加到向量a的开头
insert!(a, 3, 2) # 将2添加到向量a的第3个位置
append!(a,b) # 将向量b添加到向量a的末尾
vcat(a, b) #合并a，b 无返回值
# ---------------------改-------------------
replace!(b, 1 => 0, 4 => 3, count = 2) #替换，count替换次数上限
filter
# ---------------------筛选-------------------
v3 = [2, 2, 3, 3, 5, 11]
#删除不满足条件的元素，也就是只保留true
filter(x -> x > 5, v3)
unique(v3) # 去重
sort
v = [3,3,6,7,2,1,9]
sort(v, rev=true) # R: sort(v,decreasing = T)
sortperm(v) # R: order(v,decreasing = T)
reverse(v)
repeat
repeat(1:2, inner=3) # 1 1 1 2 2 2
repeat(1:2, outer=3) # 1 2 1 2 1 2
repeat(1:2, 3) # default outer
repeat(1:2, inner=[3,5]) # matrix
repeat(1:2, outer=[3,5]) # matrix
repeat(1:2,3,5) # 3行5列
Math
maximum(v) # 求最大值 R：max(v)
minimum(v)
argmax(v) # 求最大值首次出现的下标
argmin(v)
findmax(v) # 返回最值和相应的首次出现的下标
findmin(v)
v=[1,2,3]
sum(v)
prod(v) #求乘积
# 对于布尔型数组
all([true,false,true]) # 判断所有元素为真
any([true,false,true]) # 判断存在真值元素
[1,2,"A"] == [1,2,'A'] # 两个等长数组的对应元素是否完全相同
Matrix
Create
m = [1 2 3; 4 5 6]
size(m) # nrow, ncol
size(m,1) # nrow
size(m,2) # ncol
m = reshape(1:6, 2, 3)
初始化
zeros(2,3)
ones(Int64, 2, 3)
ones(String, 2, 3)
Array{Float64}(undef, 2, 3)
similar(m)* # 生成元素类型和大小都与m相同， 但是元素未初始化的数组*
合并
m1 = [1 2 3; 4 5 6]
m2 = [7 8 9; 1 2 3]
hcat(m1,m2) # R: cbind(m1,m2)
vcat(m1,m2) # R: rbind(m1,m2)
Retrieve
A1[2,3]
A1[2,3] = -6 # mutate
A1[:, 2] # vectror
A1[2, :] # vectror
A1[1:2, 2:3] # matrix
A1[1:2, 2:3] = [102 103; 202 203] # mutate
对每行或每列的操作
m1 = [1 2 3; 4 5 6]
mapslices(sum, m1, dims=1) # R: apply(m1,1,sum)
[sum(x) for x in eachrow(m1)]
mapslices(sum, m1, dims=2) # R: apply(m1,2,sum)
[sum(x) for x in eachcol(m1)]
转置
# R: t(m1)
# Python: m1.T; m1.transpose()
m1' == transpose(m1)
tuple
(1, "John", 5.1) # ，标识
tn1 = (name="John", age=32) # named tuple
tn1[:name] # Retrieve
tn1.name # Retrieve
Pair
x = "apple" => 1
first(x)=="apple"
last(x)==1
dictionary
Create
d = Dict("name" => "Li Ming", "age" => 18)
d2orig = [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
d2 = Dict(d2orig)
x = ['a', 'b', 'c', 'd']
y = [1,2,3,4]
d2 = Dict(zip(x, y)) #x,y是等长的数组
# ----------------------指定类型---------------------
Dict{String, Int64}("apple" => 1, "pear" => 2, "orange" => 3) #指定类型
# ----------------------字典生成器----------------------
Dict(x => x*x for x in [2,3,5,7])
Retrieve
d["age"]
get(d,"age",0) # 不存在age返回0
get!(d, "age",0)#不存在age，则add
# ----------------------键值是否存在----------------------
haskey(d, "gender")
"gender" in keys(d)
d["gender"] = "Male" # add
delete!(d, "gender") #delete "gender"
遍历
# ----------------------遍历key----------------------
for k in keys(d2)
println(k, " => ", d2[k])
end
# ----------------------遍历value----------------------
values(d2)
collect(values(d2)) # vector
# ----------------------二元遍历----------------------
for (k,v) in d2
println(k, " => ", v)
end
Set
Create
Set(1:3)
Set(['a', 'b', 'c', 'b']) #去重
Set("keep") # 'k''e''p' # Set{Char} with 3 elements
Set(["keep"]) # "keep" # Set{String} with 1 element
methods
union(A, B) #或A ∪ B：并集。∪输入为\cup
intersect(A, B) # A ∩ B: 交集。∩输入为\cap<TAB>。
setdiff(A, B) #或A \ B：差集。
issetequal(A, B) # 集合相等
issubset(A, B) # 或A ⊆ B #子集，⊆输入为\subseteq<TAB>。
#属于关系用in, ∈(\in+TAB)，∉(\notin+TAB)
push!(x, a) # 元素a加入到集合x中
