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.