A space efficient direct access data structure

Given a file T, we suggest a data structure based on pruning a Huffman shaped Wavelet tree (WT) according to the underlying skeleton Huffman tree that enables direct access to the i-th element of T. This pruned WT is especially designed to support faster random access and save memory storage, at the price of less effective rank and select operations, as compared to the original Huffman shaped WT. The savings are significant only if the underlying alphabet is large enough. We give empirical evidence that when memory storage is of main concern, our suggested data structure generally outperforms other direct access techniques such as those due to Külekci, DACs and sampling, with a slowdown as compared to DACs and fixed length encoding.