     
     private var uniqueValuesDict: Dictionary<AnyHashable, Int> = Dictionary()
 
-    lazy private var parallelExecution = ParallelExecution()
+    private let parallelExecution: ParallelExecution
     private var arrayRanges: ArrayRanges?
 
     /// Set up with the unique values

            threadCount = osThreadCount > 1 ? osThreadCount : 4

            operationQueue.maxConcurrentOperationCount = threadCount
        }
    }


    }

    private init() {
        parallelExecution = ParallelExecution()
    }

    /// Add a feature vector to the index matrix
