# Multidimensional array - search for relationships

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• Author
• Posted on
Hi All,
I have a multidimensional array where each sub-array contains just two
entries, which indicates a relationship between those two entries. for
example the first sub-array:
[0] => Array
(
[0] => 30
[1] => 31
)

This states that value 30 is related to 31. I would like to search
through the entire multidimensional array (it could be empty or
contain hundreds of entries), to see if multiple relationships exist
and hence group these relationships into one entry. so for the array
below:

Array
(
[0] => Array
(
[0] => 30
[1] => 31
)

[1] => Array
(
[0] => 29
[1] => 26
)

[2] => Array
(
[0] => 29
[1] => 27
)

[3] => Array
(
[0] => 29
[1] => 28
)

[4] => Array
(
[0] => 26
[1] => 27
)

[5] => Array
(
[0] => 27
[1] => 28
)
)

This should be represented as:
Array
(
[0] => Array
(
[0] => 30
[1] => 31
)

[1] => Array
(
[0] => 29
[1] => 26
[2] => 27
[3] => 28
)
)

I am new enough to PHP so I would appreciate your help.
Thanks

## Re: Multidimensional array - search for relationships

LittleCake wrote:

while not exactly your solution, the following code will parse the first
array to another array that looks like:

Array
(
[29] => Array
(
[0] => 26
[1] => 27
[2] => 28
)

[30] => Array
(
[0] => 31
)
)

i.e. the array index would be the index term, and the sub-array would
contain all the terms that are related to the index term.

\$result_array=array();
foreach (\$master_array as \$sub_array)
\$result_array[][]=\$sub_array[1];

MW

## Re: Multidimensional array - search for relationships

Keep the flag flying.
Shane

## Re: Multidimensional array - search for relationships

Shane is given an edge array (\$aEdges) and wants to
know the distinct connected components.  This can be done
by my function connectedComponents(\$aEdges).  The first
part walks each edge once to build an adjacency array.
The second part, which does the real work, picks an
unvisited edge and visits each vertex it can get to from
that selected vertex, processing each edge once, so that
the total running time is O(E).  It'd be O(V+E) for the
second part, if singletons (isolated vertices) were
to have been allowed.

Csaba Gabor from Vienna

function connectedComponents (\$aEdges) {
// given an edge array, \$aEdges, this will return an array
// of connected components.  Each element of the returned
// array, \$aTrees, will correspond to one component and
// have an array of the vertices in that component.
\$aAdj = array(); \$aTree = array(); \$ctr=-1;
foreach (\$aEdges as \$br)        // Construct V/E adjacancy array
foreach (\$br as \$i=>\$v) {

foreach (\$aAdj as \$v => &\$aTrees[++\$ctr])  // Now build distinct
for (\$i=0;\$i<sizeof(\$aTrees[\$ctr]);++\$i) {       // components
\$aV = array_keys(array_flip(array_merge(

return \$aTrees; }

//Example usage:
\$aEdges = array(array (30, 31), array (29, 26),
array (29, 27), array (29, 28),
array (26, 27), array (27, 28));
\$aComponents = connectedComponents (\$aEdges);

//Example 2:
\$aEdges = array(
array (a, b), array (b, d), array (b, e),
array (d, g), array (c, i), array (e, h),
array (h, j), array (c, f), array (f, i),
array (g, j), array (j, k), array(j, b));
\$aComponents = connectedComponents (\$aEdges);

## Re: Multidimensional array - search for relationships

Csaba Gabor wrote:

Whoops, small typo, though code works as is.
In the initialization it should be \$aTrees = array();

Note to self:  the determine distinct connected components
section also works with:

// determine connected components from adjacency matrix:
// \$aAdj: [\$v => array of vertices connected to \$v, ...]
foreach (\$aAdj as \$v => &\$aTrees[++\$ctr])    // Now build distinct
for (\$i=0;\$i<sizeof(\$aV=&\$aTrees[\$ctr]);++\$i)      // components