The Burrows–Wheeler transform (BWT, also called block-sorting compression) rearranges a character string into runs of similar characters. 

This is useful for compression, since it tends to be easy to compress a string that has runs of repeated characters by techniques such as move-to-front transform and run-length encoding. 

More importantly, the transformation is reversible, without needing to store any additional data. 

The BWT is thus a "free" method of improving the efficiency of text compression algorithms, costing only some extra computation.


Source: [[wp:Burrows–Wheeler_transform|Burrows–Wheeler transform]]
<br><br>