add SquareGrid layout

Author: hexaeder

docs/src/index.md

@@ -142,6 +142,17 @@ f, ax, p = graphplot(g, layout=layout)
 hidedecorations!(ax); hidespines!(ax); ax.aspect = DataAspect(); f #hide
 ```
 
+## SquareGrid Layout
+```@docs
+SquareGrid
+```
+```@example layouts
+g = path_graph(21)
+layout = SquareGrid(skip=[(1,2), (3,4)])
+f, ax, p = graphplot(g, layout=layout, nlabels=repr.(1:21), nlabels_textsize=15)
+hidedecorations!(ax); hidespines!(ax); ax.aspect = DataAspect(); f #hide
+```
+
 ## Spectral
 ```@docs
 Spectral

src/NetworkLayout.jl

@@ -85,5 +85,6 @@ include("stress.jl")
 include("spectral.jl")
 include("circular.jl")
 include("shell.jl")
+include("squaregrid.jl")
 
 end

src/squaregrid.jl

@@ -0,0 +1,57 @@
+export SquareGrid
+
+"""
+    SquareGrid(; kwargs...)(adj_matrix)
+    layout(algo::SquareGrid, adj_matrix)
+
+Position nodes on a 2 dimensional rectagular grid. The nodes are palced in order
+from upper left to lower right. To skip positions see `skip` argument.
+
+Takes adjacency matrix representation of a network and returns coordinates of
+the nodes.
+
+## Keyword Arguments
+- `Ptype=Float64`: Determines the output type `Point{2,Ptype}`
+- `cols=:auto`: Columns of the grid, the rows are determined automatic. If `:auto` the layout will be square-ish.
+- `dx=Ptype(1), dy=Ptype(-1)`: Ofsets between rows/cols.
+- `skip=Tuple{Int,Int}[]`: Specify positions to skip when placing nodes.
+  `skip=[(i,j)]` means to keep the position in the `i`-th row and `j`-th column
+  empty.
+"""
+struct SquareGrid{Ptype,CT} <: AbstractLayout{2,Ptype}
+    cols::CT
+    dx::Ptype
+    dy::Ptype
+    skip::Vector{Tuple{Int,Int}}
+end
+
+function SquareGrid(; Ptype=Float64, cols=:auto, dx=Ptype(1), dy=Ptype(-1), skip=Tuple{Int,Int}[])
+    return SquareGrid{Ptype,typeof(cols)}(cols, dx, dy, skip)
+end
+
+function layout(algo::SquareGrid{Ptype}, adj_matrix::AbstractMatrix) where {Ptype}
+    N = size(adj_matrix, 1)
+    M = N + length(algo.skip)
+
+    if algo.cols === :auto
+        cols = 0
+        while (cols^2 < M)
+            cols += 1
+        end
+    else
+        cols = algo.cols
+    end
+
+    positions = Vector{Point2{Ptype}}(undef, N)
+
+    n = 1
+    for j in 1:typemax(Int), i in 1:cols
+        if (j, i) ∉ algo.skip
+            positions[n] = Point2{Ptype}((i - 1) * algo.dx, (j - 1) * algo.dy)
+            n += 1
+            n > N && break
+        end
+    end
+
+    return positions
+end

test/runtests.jl

@@ -245,4 +245,33 @@ jagmesh_adj = jagmesh()
             @test typeof(locs) == Vector{Point{2,Float64}}
         end
     end
+
+    @testset "Testing Square Grid Layout" begin
+        println("SquareGrid")
+        @testset "Testing col length" begin
+            M = adjacency_matrix(SimpleGraph(4))
+            positions = SquareGrid(; Ptype=Int)(M)
+            @test positions == Point2.([(0, 0), (1, 0), (0, -1), (1, -1)])
+
+            M = adjacency_matrix(SimpleGraph(3))
+            positions = SquareGrid(; Ptype=Int)(M)
+            @test positions == Point2.([(0, 0), (1, 0), (0, -1)])
+
+            M = adjacency_matrix(SimpleGraph(5))
+            positions = SquareGrid(; Ptype=Int, cols=2)(M)
+            @test positions == Point2.([(0, 0), (1, 0), (0, -1), (1, -1), (0, -2)])
+        end
+
+        @testset "Testing dx,dy" begin
+            M = adjacency_matrix(SimpleGraph(4))
+            positions = SquareGrid(; Ptype=Int, dx=2, dy=3)(M)
+            @test positions == Point2.([(0, 0), (2, 0), (0, 3), (2, 3)])
+        end
+
+        @testset "Testing skip" begin
+            M = adjacency_matrix(SimpleGraph(4))
+            positions = SquareGrid(; Ptype=Int, skip=[(1, 1), (2, 2)])(M)
+            @test positions == Point2.([(1, 0), (2, 0), (0, -1), (2, -1)])
+        end
+    end
 end