Julia -- 10-5（配列）

配列の要素が true のもののインデックスを取り出す　　findall(), findall(f::Function, A)

julia> A = [true, false, false, true]
4-element Array{Bool,1}:
 1
 0
 0
 1

julia> findall(A)
2-element Array{Int64,1}:
 1
 4

julia> A = [true false; false true]
2×2 Array{Bool,2}:
 1  0
 0  1

julia> findall(A)
2-element Array{CartesianIndex{2},1}:
 CartesianIndex(1, 1)
 CartesianIndex(2, 2)

julia> findall(falses(3))
Int64[]

julia> x = [1, 3, 4]
3-element Array{Int64,1}:
 1
 3
 4

julia> findall(isodd, x)
2-element Array{Int64,1}:
 1
 2

julia> A = [1 2 0; 3 4 0]
2×3 Array{Int64,2}:
 1  2  0
 3  4  0
julia> findall(isodd, A)
2-element Array{CartesianIndex{2},1}:
 CartesianIndex(1, 1)
 CartesianIndex(2, 1)

julia> findall(!iszero, A)
4-element Array{CartesianIndex{2},1}:
 CartesianIndex(1, 1)
 CartesianIndex(2, 1)
 CartesianIndex(1, 2)
 CartesianIndex(2, 2)

julia> d = Dict(:A => 10, :B => -1, :C => 0)
Dict{Symbol,Int64} with 3 entries:
  :A => 10
  :B => -1
  :C => 0

julia> findall(x -> x >= 0, d)
2-element Array{Symbol,1}:
 :A
 :C

最初に見つかる true のインデックスを返す　　findfirst(A), findfirst(predicate::Funciton, A)

julia> A = [false, false, true, false]
4-element Array{Bool,1}:
 0
 0
 1
 0

julia> findfirst(A)
3

julia> findfirst(falses(3)) # returns nothing, but not printed in the REPL

julia> A = [false false; true false]
2×2 Array{Bool,2}:
 0  0
 1  0

julia> findfirst(A)
CartesianIndex(2, 1)

julia> A = [1, 4, 2, 2]
4-element Array{Int64,1}:
 1
 4
 2
 2

julia> findfirst(iseven, A)
2

julia> findfirst(x -> x>10, A) # returns nothing, but not printed in the REPL

julia> findfirst(isequal(4), A)
2

julia> A = [1 4; 2 2]
2×2 Array{Int64,2}:
 1  4
 2  2

julia> findfirst(iseven, A)
CartesianIndex(2, 1)

最後に見つかる true のインデックスを返す　　findlast(A), findlast(predicate::Function, A)

julia> A = [true, false, true, false]
4-element Array{Bool,1}:
 1
 0
 1
 0

julia> findlast(A)
3

julia> A = falses(2,2);

julia> findlast(A) # returns nothing, but not printed in the REPL

julia> A = [true false; true false]
2×2 Array{Bool,2}:
 1  0
 1  0

julia> findlast(A)
CartesianIndex(2, 1)

julia> A = [1, 2, 3, 4]
4-element Array{Int64,1}:
 1
 2
 3
 4

julia> findlast(isodd, A)
3

julia> findlast(x -> x > 5, A) # returns nothing, but not printed in the REPL

julia> A = [1 2; 3 4]
2×2 Array{Int64,2}:
 1  2
 3  4

julia> findlast(isodd, A)
CartesianIndex(2, 1)

i 以後の次の true インデックスを返す　　findnext(A, i)，findnext(predicate::Function, A, i)

julia> A = [false, false, true, false]
4-element Array{Bool,1}:
 0
 0
 1
 0

julia> findnext(A, 1)
3

julia> findnext(A, 4) # returns nothing, but not printed in the REPL

julia> A = [false false; true false]
2×2 Array{Bool,2}:
 0  0
 1  0

julia> findnext(A, CartesianIndex(1, 1))
CartesianIndex(2, 1)

julia> A = [1, 4, 2, 2];

julia> findnext(isodd, A, 1)
1

julia> findnext(isodd, A, 2) # returns nothing, but not printed in the REPL

julia> A = [1 4; 2 2];

julia> findnext(isodd, A, CartesianIndex(1, 1))
CartesianIndex(1, 1)

i 以前の true インデックスを返す　　findprev(A, i)，findprev(predicate::Function A, i)

julia> A = [false, false, true, true]
4-element Array{Bool,1}:
 0
 0
 1
 1

julia> findprev(A, 3)
3

julia> findprev(A, 1) # returns nothing, but not printed in the REPL

julia> A = [false false; true true]
2×2 Array{Bool,2}:
 0  0
 1  1

julia> findprev(A, CartesianIndex(2, 1))
CartesianIndex(2, 1)

julia> A = [4, 6, 1, 2]
4-element Array{Int64,1}:
 4
 6
 1
 2

julia> findprev(isodd, A, 1) # returns nothing, but not printed in the REPL

julia> findprev(isodd, A, 3)
3

julia> A = [4 6; 1 2]
2×2 Array{Int64,2}:
 4  6
 1  2

julia> findprev(isodd, A, CartesianIndex(1, 2))
CartesianIndex(2, 1)

対角要素を中心に右上と左下を入れ替える　　permutedims(m)

転置 transpose とは異なる。

julia> a = [1 2; 3 4];

julia> b = [5 6; 7 8];

julia> c = [9 10; 11 12];

julia> d = [13 14; 15 16];

julia> X = [[a] [b]; [c] [d]]
2×2 Array{Array{Int64,2},2}:
 [1 2; 3 4]     [5 6; 7 8]
 [9 10; 11 12]  [13 14; 15 16]

julia> permutedims(X)
2×2 Array{Array{Int64,2},2}:
 [1 2; 3 4]  [9 10; 11 12]
 [5 6; 7 8]  [13 14; 15 16]

julia> transpose(X)
2×2 Transpose{Transpose{Int64,Array{Int64,2}},Array{Array{Int64,2},2}}:
 [1 3; 2 4]  [9 11; 10 12]
 [5 7; 6 8]  [13 15; 14 16]

julia> permutedims([1, 2, 3, 4])
1×4 Array{Int64,2}:
 1  2  3  4

julia> V = [[[1 2; 3 4]]; [[5 6; 7 8]]]
2-element Array{Array{Int64,2},1}:
 [1 2; 3 4]
 [5 6; 7 8]

julia> permutedims(V)
1×2 Array{Array{Int64,2},2}:
 [1 2; 3 4]  [5 6; 7 8]

julia> transpose(V)
1×2 Transpose{Transpose{Int64,Array{Int64,2}},Array{Array{Int64,2},1}}:
 [1 3; 2 4]  [5 7; 6 8]

コピーを伴わない permutedims　　PermuteDimsArray(A, perm) -> B

julia> A = rand(3,5,4);

julia> B = PermutedDimsArray(A, (3,1,2));

julia> size(B)
(4, 3, 5)

julia> B[3,1,2] == A[1,2,3]
true

次元属性が一致するかどうか　　promote_shape(s1, s2)

julia> a = fill(1, (3,4,1,1,1));

julia> b = fill(1, (3,4));

julia> promote_shape(a,b)
(Base.OneTo(3), Base.OneTo(4), Base.OneTo(1), Base.OneTo(1), Base.OneTo(1))

julia> promote_shape((2,3,1,4), (2, 3, 1, 4, 1))
(2, 3, 1, 4, 1)