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Lecture 3: Data and Project Management

Rasi Subramaniam

Link to slides

Reminders

The homework assignment is available today (October 6) and is due October 13 at 3:20pm.

Learning objectives

  • Identify minimum requirements for a reproducible computational project
  • Apply good practices for file organization
  • Use tidy principles for tabular (spreadsheet-style) data

Outline

  1. Elements of reproducibility
  2. File organization
  3. Tidy data

This class requires Microsoft Excel or LibreOffice Calc (for opening .xlsx or .csv files).

Minimum elements for computational reproducibility

  • Annotated data from experiments or simulations
  • Documented code for data analyses
  • Defined software environments
  • Standardized organization of above 3 elements

1 project = 1 GitHub repository

  • Code
  • Data*
  • Lab notebook
  • Presentations
  • Manuscripts
  • Grants & fellowships
  • Discussion

Different locations for data at different analysis stages

  • Raw data: can be very large, store in cloud eg. AWS S3 or public repositories eg. Zenodo, SRA
  • Intermediate data: can be large or small, store in temporary scratch space
  • Tables underlying figures or samples: small, store in GitHub

Store sample annotations with data

Raw data without annotations cannot be analyzed

data/sample1.fastq
data/sample2.fastq
data/sample3.fastq
data/sample_annotations.tsv

sample1.fastq

@SRR21277963.1
GGAGTAACAGAAGTGAGAACCAGCTTATCAGAAAAAAAGTTTGAATTATG
+SRR21277963.1
AAGAGGGGAGGGAGGGGIAGGGGGGA.GGGGAGGGGIGIGGII<A<GGAA

sample_annotations.tsv

sample  srr_id       sample_id  sample_name
sample1 SRR21277963  104p8      dicodon_facs_off_low_2
sample2 SRR21277964  104p7      dicodon_facs_off_high_2
sample3 SRR21277965  104p6      dicodon_facs_on_low_2

Benefits of GitHub

  • Version control (file history, track changes)
  • Collaboration (branches, merging, issue comments, discussion)
  • Project management tools (project board, issues, milestones, labels)
  • Link to Slack channel for notifications

Organization of GitHub repository

project_name
  |-- analysis/
  |-- experiments/
  |-- grants/
  |-- presentations/
  |-- manuscripts/
  |-- .devcontainer/
  |-- .gitignore
  |-- README.md
  • Use README.md to give an overview of the project and file organization
  • Use .gitignore to ignore files that should not be tracked by git
  • Use .devcontainer/ to define the software environment for analysis (specific to VSCode), also called .install/

Organization of analysis folder

analysis
    |--USER
        |--ANALYSIS_TYPE (eg. riboseq)
            |--YYYY-MM-DD_short_desc
                |--README.md
                |--data 
                    |--gencode
                        |--gencode.v26.gtf.gz
                    |--fastq
                        |--SRRnnnnnn.fastq
                |--scripts
                    |--analyze_riboseq.ipynb
                    |--download_from_sra.ipynb
                    |--run_analysis_pipeline.smk
                |--annotations 
                    |--sample_annotations.csv
                |--tables
                    |--summary_table_1.csv
                    |--summary_table_2.csv
                |--figures
                    |--summary_figure_1.pdf
                    |--summary_figure_2.pdf
  • .gz and .fastq files are usually in .gitignore
  • README.md should give an overview of the analysis, data source etc. and how to reproduce it
  • Ideally, every data file should be downloaded programmatically from permalinks

Naming conventions

  • Project repo: Short, descriptive, understandable
  • File names
    • No caps, no spaces, no special characters other than _ and -
    • Date format: YYYY-MM-DD
    • No version numbers or names such as rasi_v20 (GitHub does this automatically)
  • Experiment labels
    • exp001, exp002 etc.
    • Use in filenames, sample annotations, issues
  • Sample labels
    • 16p1, 16p2 ... 20t1, 20t2 etc...
    • Include experiment number (16, 20), type of sample (p, t), and sample number (1, 2)
    • Use on Eppendorf tubes, lab notebook etc.
    • Create a table of sample annotations in your lab notebook record
Documenting data can be a time-consuming process, but is often required to submit data to repositories. Since data publishing is a requirement for most academic research as a part of publication, keeping track of this information early on can save you time later, and increase the chances of other researchers using your data later (which means more citations for you).

Tidy data

A standard method of displaying a multivariate set of data is in the form of a data matrix in which rows correspond to sample individuals and columns to variables, so that the entry in the ith row and jth column gives the value of the jth variate as measured or observed on the ith individual.

  1. Each variable forms a column
  2. Each observation forms a row
  3. Each type of observational unit forms a table
Data in this form is much easier to deal with programmatically. This is also known as a _data frame_. See [this](https://r4ds.had.co.nz/tidy-data.html) tutorial for an `R`-centric overview of tidy data.

Tidy data examples

Saving data as plain text files is necessarily to process this data with either R or Python. You can export from Excel to .tsv (tab-delimited, preferred format) or .csv (comma-delimited). A few things to note when exporting data files in these formats:

  • Beware that line endings differ between Windows and Unix (including Mac), though the text editors we recommend for this class can deal with this
  • Exporting from Excel only works for the currently displayed spreadsheet. If you have multiple sheets, you'll need to export multiple times.

Exercise on tidy data

Split into small groups of 3-4 people to work from an HI (haemagglutination-inhibition) table and convert to tidy data. Data available as an Excel table in the course repo.

Further reading