function filter_extract ($v, $field = 'id')
  {
    return map ($v, function ($e) use ($field) {
      return getField ($e, $field);
    });
  }
function filter_extract ($v, $field = 'id')
  {
    return map ($v, function ($e) use ($field) {
      return getField ($e, $field);
    });
  }
function filter_extract ( $ v , $ field = 'id' ) { return map ( $ v , function ( $ e ) use ( $ field ) { return getField ( $ e , $ field ) ; } ) ; }
Extracts a field from a list of arrays or objects and returns an array, with the same cardinality, containing that
field's values.

><p>You may use the `join` filter to generate a string from the resulting array.

@param array|\Traversable $v
@param string             $field The name of the field to be extracted.
@return string
Extracts a field from a list of arrays or objects and returns an array with the same cardinality containing that field s values .