Often, it is desirable to launch a DNAnexus application or workflow on many files automatically. One approach to batch processing is to write a short script to loop over the desired files in a project and launch jobs or analyses. Alternatively, the DNAnexus SDK provides a few handy utilities for batch processing.
In this tutorial, we'll batch process a series of sample FASTQs, forward and reverse reads. We'll use the
dx generate_batch_inputs command to generate a batch file, a tab-delimited (TSV) file where each row corresponds to a single run in our batch. Then we'll process our batch using the
dx run command with the
Generate Batch File
In the project My Research Project we have the following files in our root directory:
$ dx select "My Research Project"
Selected project My Research Project
$ dx ls /
We want to batch process these read pairs using BWA-MEM (requires login). For a single execution of the BWA-MEM app we need to specify the following inputs:
reads_fastqgz - FASTQ containing the left mates
reads2_fastqgz - FASTQ containing the right mates
genomeindex_targz - BWA reference genome index
We'll use the BWA reference genome index from the public Reference Genome (requires login) project for all runs; however, for the forward and reverse reads we want read pairs used to vary from run to run. To generate a batch file that pairs our input reads:
$ dx generate_batch_inputs -ireads_fastqgz='RP(.*)_R1_(.*).fastq.gz' -ireads2_fastqgz='RP(.*)_R2_(.*).fastq.gz'
Found 4 valid batch IDs matching desired pattern.
Created batch file dx_batch.0000.tsv
CREATED 1 batch files each with at most 500 batch IDs.
You can optionally provide a --path argument and provide a specific file and folder to search for recursively within your project. Specifically, the value for --path must be a directory specified as:
/path/to/directory or project-xxxx:/path/to/directory
Any file present within this directory or recursively within any subdirectory of this directory will be considered a candidate for a batch run.
(.*) are regular expression groups. You can provide arbitrary regular expressions as input. The first match in the group will be the pattern used to group pairs in the batch, these matches are called batch identifiers (batch IDs). To explain this behavior in more detail, We will use the output of the
dx generate_batch_inputs command above:
dx generate_batch_inputs command creates the
dx_batch.0000.tsv that looks like:
$ cat dx_batch.0000.tsv
batch ID reads_fastqgz reads2_fastqgz pair1 ID pair2 ID
10B_S1 RP10B_S1_R1_001.fastq.gz RP10B_S1_R2_001.fastq.gz file-aaa file-bbb
10T_S5 RP10T_S5_R1_001.fastq.gz RP10T_S5_R2_001.fastq.gz file-ccc file-ddd
15B_S4 RP15B_S4_R1_002.fastq.gz RP15B_S4_R2_002.fastq.gz file-eee file-fff
15T_S8 RP15T_S8_R1_002.fastq.gz RP15T_S8_R2_002.fastq.gz file-ggg file-hhh
Recall the regular expression was
RP(.*)_R1_(.*).fastq.gz. Although there are two grouped matches in this example, only the first one is used as the pattern for the batch ID. For example, the pattern identified for
10B_S1 which corresponds to the first grouped match while the second one is ignored.
Examining the TSV file above, the files are grouped as expected, with the first match labeling the identifier of the group within the batch. The next two columns show the file names. The last two columns contain the IDs of the files on the DNAnexus platform. You can either edit this file directly or import it into a spreadsheet to make any subsequent changes.
Note that the example above is for a case where all files are be paired properly.
dx generate_batch_inputs will create a TSV for all files that can be successfully matched for a particular batch ID. There are two classes of errors for batch IDs that are not successfully matched:
- A particular input is missing (e.g.
reads_fastqgz has a pattern but no corresponding match can be found for
- More than one file ID matches the exact same name
For both of these cases,
dx generate_batch_inputs returns a description of these errors to STDERR.
If you match more than 500 files, multiple batch files will be generated in groups of 500 to limit the number of jobs in a single batch run.
Run a batch job
We have our batch file so now we can execute our BWA-MEM batch process:
$ dx run bwa_mem_fastq_read_mapper -igenomeindex_targz="Reference Genome Files":"/H. Sapiens - GRCh38/GRCh38.no_alt_analysis_set.bwa-index.tar.gz" --batch-tsv dx_batch.0000.tsv
genomeindex_targz is a parameter set at execution time that is common to all groups in the batch and
--batch-tsv corresponds to the input file generated above.
To monitor a batch job, simply use the 'Monitor' tab like you normally would for jobs you launch.
Seting output folders for batch jobs
In order to direct the output of each run into a separate folder, the
--batch-folders flag can be used, for example:
$ dx run bwa_mem_fastq_read_mapper -igenomeindex_targz="project-BQpp3Y804Y0xbyG4GJPQ01xv:file-BFBy4G805pXZKqV1ZVGQ0FG8" --batch-tsv dx_batch.0000.tsv --batch-folders
This will output the results for each sample in folders named after batch IDs, in our case the folders: "/10B_S1/", "/10T_S5/", "/15B_S4/", and "/15T_S8/". If the folders do not exist, they will be created.
The output folders are created under a path defined with
--destination, which by default is set to current project and the "/" folder. For example, this command will output the result files in "/run_01/10B_S1/", "/run_01/10T_S5/", etc.:
$ dx run bwa_mem_fastq_read_mapper -igenomeindex_targz="project-BQpp3Y804Y0xbyG4GJPQ01xv:file-BFBy4G805pXZKqV1ZVGQ0FG8" --batch-tsv dx_batch.0000.tsv --batch-folders --destination="My_project":/run_01"