6.3.1.1. sort-bed

The sort-bed utility sorts BED files of any size, even larger than system memory. BED files that are in lexicographic-chromosome order allow BEDOPS utilities to work efficiently with data from any species without software modifications. Further, sorted files can be traversed very quickly.

Sorted BED order is defined first by lexicographic chromosome order, then ascending integer start coordinate order, and finally by ascending integer end coordinate order. To make the sort order unambiguous, a lexicographical sort is applied on fourth and subsequent columns, where present in the input BED dataset.

Other utilities in the BEDOPS suite require data in sorted order as described. You only need to sort once: BEDOPS utilities all read and write data in sorted order.

6.3.1.1.1. Migrating older BED and Starch files

The utility update-sort-bed-migrate-candidates recursively locates BED and pre-v2.4.20 Starch files in the specified parent directory, tests if they require re-sorting to conform to the updated, post-v2.4.20 ‘sort-bed’ order, and offers actions to log candidate files, or immediately apply a resort action that is performed locally or via a SLURM-managed cluster.

The convenience utilities update-sort-bed-slurm and update-sort-bed-starch-slurm update the sort order of BED or Starch files sorted with pre-v2.4.20 sort-bed via a SLURM-based cluster. See update-sort-bed-slurm --help or update-sort-bed-starch-slurm --help for more details. These utilities can be used standalone or in conjunction with the update-sort-bed-migrate-candidates utility.

6.3.1.1.2. Inputs and outputs

6.3.1.1.2.1. Input

The sort-bed utility requires one or more three-column BED file(s). Support for common headers (such as UCSC BED track headers) is included, although headers will be stripped from the output.

6.3.1.1.2.2. Output

The sort-bed utility sends sorted BED data to standard output, which can be redirected to a file or piped to other utilities, including core BEDOPS utilities like bedops and bedmap. Sort order is defined by a lexicographical sort on chromosome name, a numerical sort on start coordinates, a numerical sort on stop coordinates where there are start matches, and finally a lexicographical sort on the remainder of the BED element (if additional columns are present).

6.3.1.1.3. Usage

The --help option is fairly basic, but describes the usage:

sort-bed
  citation: http://bioinformatics.oxfordjournals.org/content/28/14/1919.abstract
  version:  2.4.28
  authors:  Scott Kuehn

USAGE: sort-bed [--help] [--version] [--check-sort] [--max-mem <val>] [--tmpdir <path>] <file1.bed> <file2.bed> <...>
        Sort BED file(s).
        May use '-' to indicate stdin.
        Results are sent to stdout.

        <val> for --max-mem may be 8G, 8000M, or 8000000000 to specify 8 GB of memory.
        --tmpdir is useful only with --max-mem.

A simple example of using sort-bed would be:

$ sort-bed unsortedData.bed > sortedData.bed

The sort-bed program efficiently sorts BED inputs. By default, all input records are read into system memory and sorted. If your BED dataset is larger than available system memory, use the --max-mem option to limit the amount of memory sort-bed uses to do its work:

$ sort-bed --max-mem 2G reallyHugeUnsortedData.bed > reallyHugeSortedData.bed

This option allows sort-bed to scale to input of any size.

The --tmpdir option allows specification of an alternative temporary directory, when used in conjunction with --max-mem option. This is useful if the host operating system’s standard temporary directory (e.g., /tmp on Linux or OS X) does not have sufficient space to hold intermediate results.

For example, to use the current working directory to store temporary data, one could use the $PWD environment variable:

$ sort-bed --max-mem 2G --tmpdir $PWD reallyHugeUnsortedData.bed > reallyHugeSortedData.bed

Use of the --check-sort option returns a message if the input is sorted, or not.