nearest
Nearest neighbors within radius
Description
uses additional options specified by one or more namevalue pair arguments. For
example, if nodeIDs
= nearest(G
,s
,d
,Name,Value
)G
is a weighted graph, then
nearest(G,s,d,'Method','unweighted')
ignores the edge weights
in graph G
and instead treats all edge weights as
1
.
Examples
Nearest Nodes
Create and plot a graph with weighted edges.
s = [1 1 1 1 1 2 2 2 3 3 3 3 3]; t = [2 4 5 6 7 3 8 9 10 11 12 13 14]; weights = randi([1 10],1,13); G = graph(s,t,weights); p = plot(G,'Layout','force','EdgeLabel',G.Edges.Weight);
Determine which nodes are within a radius of 15 from node 1.
nn = nearest(G,1,15)
nn = 9×1
5
7
2
3
4
6
8
12
9
Highlight the source node as green and the nearest neighbors as red.
highlight(p,1,'NodeColor','g') highlight(p,nn,'NodeColor','r')
Distances of Nearest Nodes
Create and plot a graph with weighted edges.
s = [1 1 1 2 2 6 6 7 7 3 3 9 9 4 4 11 11 8];
t = [2 3 4 5 6 7 8 5 8 9 10 5 10 11 12 10 12 12];
weights = [10 10 10 10 10 1 1 1 1 1 1 1 1 1 1 1 1 1];
G = graph(s,t,weights);
plot(G,'EdgeLabel',G.Edges.Weight)
Determine which nodes are within a radius of 5 from node 3, and return the distance to each node.
[nn,dist] = nearest(G,3,5)
nn = 9×1
9
10
5
11
4
7
12
6
8
dist = 9×1
1
1
2
2
3
3
3
4
4
Incoming Neighbor Distances in Directed Graph
Create and plot a directed graph with weighted edges.
s = {'a' 'a' 'a' 'b' 'c' 'c' 'e' 'f' 'f'}; t = {'b' 'c' 'd' 'a' 'a' 'd' 'f' 'a' 'b'}; weights = [1 1 1 2 2 2 2 2 2]; G = digraph(s,t,weights); plot(G,'EdgeLabel',G.Edges.Weight)
Determine the nearest nodes within a radius of 1 from node 'a'
, measured by outgoing path distance from node 'a'
.
nn_out = nearest(G,'a',1)
nn_out = 3x1 cell
{'b'}
{'c'}
{'d'}
Determine all of the nodes that have incoming paths leading to node 'a'
by specifying the radius as Inf
.
nn_in = nearest(G,'a',Inf,'Direction','incoming')
nn_in = 4x1 cell
{'b'}
{'c'}
{'f'}
{'e'}
Input Arguments
s
— Source node
node index  node name
Source node, specified as a node index or a node name in one of the forms in this table.
Value  Example 

Scalar node index  1 
Character vector node name  'A' 
String scalar node name  "A" 
Example: nearest(G,3,1)
Example: nearest(G,'a',5)
d
— Neighbor distance radius
scalar
Neighbor distance radius, specified as a numeric scalar.
Example: nearest(G,3,1)
Example: nearest(G,'a',2.5)
NameValue Arguments
Specify optional
commaseparated pairs of Name,Value
arguments. Name
is
the argument name and Value
is the corresponding value.
Name
must appear inside quotes. You can specify several name and value
pair arguments in any order as
Name1,Value1,...,NameN,ValueN
.
[nodeIDs,dist] =
nearest(G,s,5,'Method','unweighted','Direction','incoming')
Direction
— Direction of distance measurement
'outgoing'
(default)  'incoming'
Note
The 'Direction'
option can only be specified
with directed graphs.
Direction of distance measurement, specified as the commaseparated
pair consisting of 'Direction'
and one of the options
in this table.
Option  Description 

'outgoing' (default)  Distances are calculated using paths going
out from source node
s . 
'incoming'  Distances are calculated using paths coming
in to source node
s . 
Example: nearest(G,s,d,'Direction','incoming')
Method
— Shortest path algorithm
'auto'
(default)  'unweighted'
 'positive'
 'mixed'
Shortest path algorithm, specified as the commaseparated pair
consisting of 'Method'
and one of the options in this
table.
Option  Description 

'auto' (default) 
The

'unweighted' 
Breadthfirst computation that treats all edge
weights as 
'positive' 
Dijkstra algorithm that requires all edge weights to be nonnegative. 
'mixed' (only for
digraph ) 
BellmanFord algorithm for directed graphs that requires the graph to have no negative cycles. While 
Note
For most graphs, 'unweighted'
is the fastest
algorithm, followed by 'positive'
and
'mixed'
.
Example: nearest(G,s,d,'Method','positive')
Output Arguments
nodeIDs
— Nearest neighbor node IDs
node indices  node names
Nearest neighbor node IDs, returned as node indices if
s
is numeric, or as node names if
s
is a node name. The nodes are sorted from nearest
to furthest. nodeIDs
is empty if no nodes are within the
specified distance. nodeIDs
never contains the source
node s
even if the graph has selfloops.
Use H = subgraph(G,[s; nodeIDs])
to extract a subgraph
of the nearest neighbors from the original graph
G
.
dist
— Neighbor distances
vector
Neighbor distances, returned as a vector. dist(j)
is
the distance from source node s
to neighboring node
nodeIDs(j)
.
See Also
shortestpath
 distances
 shortestpathtree
 neighbors
 successors
 predecessors
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