function SparseVector::correlation in Recommender API 6.2

Same name and namespace in other branches

1. 7.6 classes/Matrix.php \SparseVector::correlation()

Compute correlation with $vector. No caching option. Works for RealVector. SparseVector needs additional handling.

Parameters

$vector it has to be the same type (either SparseVector or RealVector) as $this:

Return value

correlation value

Overrides Vector::correlation

File

./Matrix.php, line 328

Class

SparseVector

Sparse Vector takes care of missing data.

Code

function correlation(&$vector) {
  $subset = $this
    ->common_items($vector);
  if ($subset === NULL) {
    return NAN;
  }
  $covariance = $subset[0]
    ->covariance($subset[1]);
  $std_a = $subset[0]
    ->std(TRUE);
  $std_b = $subset[1]
    ->std(TRUE);
  return $std_a == 0 || $std_b == 0 ? NAN : $covariance / ($std_a * $std_b);
}