Editing Bit array (section)

== Compression ==

A bit array is the most dense storage for "random" bits, that is, where each bit is equally likely to be 0 or 1, and each one is independent. But most data are not random, so it may be possible to store it more compactly. For example, the data of a typical fax image is not random and can be compressed. [[Run-length encoding]] is commonly used to compress these long streams. However, most compressed data formats are not so easy to access randomly; also by compressing bit arrays too aggressively we run the risk of losing the benefits due to bit-level parallelism ([[Array programming|vectorization]]). Thus, instead of compressing bit arrays as streams of bits, we might compress them as streams of bytes or words (see [[Bitmap index#Compression|Bitmap index (compression)]]).