Understanding Burrows Wheeler Transform
The Burrows Wheeler Transform, often called BWT, rearranges text without losing data. It does not compress data by itself. It prepares repeated characters and nearby patterns for stronger compression steps. That makes it useful before run length coding, move to front coding, and entropy coding.
Why This Calculator Helps
This calculator shows the transform in a clear, practical way. You can enter plain text, choose a sentinel symbol, and create the transformed string. You can also reverse a known transform by entering the last column and its primary index. The result block appears above the form, so the answer is easy to review before changing inputs.
How The Transform Works
BWT builds every cyclic rotation of the input. It then sorts those rotations in lexicographic order. The last character of each sorted row becomes the transformed output. The row that contains the original text gives the primary index. A unique sentinel is usually added, because it marks the true end of the string.
Reverse Transform Idea
The inverse method uses the relationship between the first column and last column. The first column is the sorted version of the transformed text. Repeated sorting can rebuild the rotation table for learning purposes. Efficient production tools use last first mapping, but the visible table method is easier to inspect.
Practical Uses
BWT is common in compression pipelines. It groups similar symbols together, which can create long runs. Those runs are easier to encode with later methods. The transform is also reversible, so the original text can be restored exactly when the correct index is known.
Good Input Tips
Use short text when you want to inspect all rotations. Long strings create large tables. Choose a sentinel that does not appear in the original input. The dollar sign is common, but any unique character can work. For decoding, copy the transformed string exactly. Also enter the primary index from the encoding result. Small changes can produce a different output.
Final Notes
This tool is designed for study, checking homework, testing examples, and building intuition. It keeps the steps visible and gives export options for records. Use the CSV button for spreadsheet work. Use the PDF button for printable summaries too.