Interesting issue with an integration between a new Salesforce application and a legacy enterprise application. The data from salesforce API was limited to 50 records at once so as a workaround the Salesforce team gave access via a SQL call which could send more records each time. Consuming the data came via GuzzleHTTP which absorbed the data from Salesforce and delivers as an object as a nested associative array. E.g.

array (
  Key1 = Value1
  Key2 = array ( 
           key3 = value3
           key4 = value4
       )
)

which would need to be unwound into dot notation for CSV export (with headers) as

key1, key2.key3, key2.key4
value1, value3, value4

The Salesforce arrays were 3+ levels deep. Not finding a array to dot notation function, I wrote the following:

/**
 * Function unwind_nested_array.
 *
 * Recursive function that creates delimited keys from nested associative array.
 *
 * @param array $data
 *   The many-leveled array to unwind into an array that is one level deep.
 * @param string $delimiter
 *   The string to use separating key values (e.g. '.')
 *
 * @return array
 *   Associative array returned as dotted of nested array.
 */
function unwind_nested_array(array $data, $delimiter = '') { 
  $result = [];
  foreach ($data as $key => $value) { 
    if (is_array($value)) { 
      $result = $result + unwind_nested_array($value, $delimiter . $key . '.');
    } 
    else { 
      $result[$delimiter . $key] = $value;
    } 
  } 
  return $result;
}