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<?php $lookup = [ ['a', 'ape'], ['b', 'bee'], ['a', 'ant'], ['d', 'dog'], ['b', 'bat'], ['a', 'asp'], ]; function getValueAt($lookup, $rowIndex, $columnIndex) { return $lookup[$rowIndex][$columnIndex]; } $columnIndex = 0; $values = []; for ($i = 0; $i < count($lookup); ++$i) { $values[getValueAt($lookup, $i, $columnIndex)][] = $i; } var_export($values); echo "\n"; $onlyRecurringRows = array_filter($values, fn($row) => count($row) > 1); var_export($onlyRecurringRows);
Output for git.master_jit, git.master, rfc.property-hooks
array ( 'a' => array ( 0 => 0, 1 => 2, 2 => 5, ), 'b' => array ( 0 => 1, 1 => 4, ), 'd' => array ( 0 => 3, ), ) array ( 'a' => array ( 0 => 0, 1 => 2, 2 => 5, ), 'b' => array ( 0 => 1, 1 => 4, ), )

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