Add drop_nodes transform (#426)

* drop node

* tests

* Update transform.jl

* Update transform.jl

* added to gnngraphs

* error in test?

* Update src/GNNGraphs/transform.jl

float32 args

Co-authored-by: Carlo Lucibello <carlo.lucibello@gmail.com>

* Update src/GNNGraphs/transform.jl

arg fix

Co-authored-by: Carlo Lucibello <carlo.lucibello@gmail.com>

---------

Co-authored-by: Carlo Lucibello <carlo.lucibello@gmail.com>

src/GNNGraphs/GNNGraphs.jl

@@ -79,6 +79,7 @@ export add_nodes,
        to_unidirected,
        random_walk_pe,
        remove_nodes,
+       drop_nodes,
 # from Flux
        batch,
        unbatch,

src/GNNGraphs/transform.jl

@@ -306,6 +306,38 @@ function remove_nodes(g::GNNGraph{<:COO_T}, nodes_to_remove::AbstractVector)
              ndata, edata, g.gdata)
 end
 
+"""
+    drop_nodes(g::GNNGraph{<:COO_T}, p)
+
+Randomly drop nodes (and their associated edges) from a GNNGraph based on a given probability. 
+Dropping nodes is a technique that can be used for graph data augmentation, refering paper [DropNode](https://arxiv.org/pdf/2008.12578.pdf).
+
+# Arguments
+- `g`: The input graph from which nodes (and their associated edges) will be dropped.
+- `p`: The probability of dropping each node. Default value is `0.5`.
+
+# Returns
+A modified GNNGraph with nodes (and their associated edges) dropped based on the given probability.
+
+# Example
+```julia
+using GraphNeuralNetworks
+# Construct a GNNGraph
+g = GNNGraph([1, 1, 2, 2, 3], [2, 3, 1, 3, 1], num_nodes=3)
+# Drop nodes with a probability of 0.5
+g_new = drop_node(g, 0.5)
+println(g_new)
+```
+"""
+function drop_nodes(g::GNNGraph{<:COO_T}, p = 0.5)
+    num_nodes = g.num_nodes
+    nodes_to_remove = filter(_ -> rand() < p, 1:num_nodes)
+
+    new_g = remove_nodes(g, nodes_to_remove)
+
+    return new_g
+end
+
 """
     add_edges(g::GNNGraph, s::AbstractVector, t::AbstractVector; [edata])
     add_edges(g::GNNGraph, (s, t); [edata])

test/GNNGraphs/transform.jl

@@ -239,6 +239,24 @@ end
     @test edata_new == edatatest
 end end
 
+@testset "drop_nodes" begin
+    if GRAPH_T == :coo
+        Random.seed!(42)
+        s = [1, 1, 2, 3]
+        t = [2, 3, 4, 5]
+        g = GNNGraph(s, t, graph_type = GRAPH_T)    
+
+        gnew = drop_nodes(g, Float32(0.5))
+        @test gnew.num_nodes == 3
+
+        gnew = drop_nodes(g, Float32(1.0))
+        @test gnew.num_nodes == 0
+
+        gnew = drop_nodes(g, Float32(0.0))
+        @test gnew.num_nodes == 5
+    end
+end
+
 @testset "add_nodes" begin if GRAPH_T == :coo
     g = rand_graph(6, 4, ndata = rand(2, 6), graph_type = GRAPH_T)
     gnew = add_nodes(g, 5, ndata = ones(2, 5))