#library("SpaDES.project")

This vignette expands upon blog posts originally posted on the Predictive Ecology website1 2.

## Project directory structure

The simplest structure is to use a single directory for all project-related components:

myProject/
|_  cache/            # use this for your simulation cachePath
|_  inputs/           # use this for your simulation inputPath
|_  manuscripts/
|_  modules/          # use this for your simulation modulePath
|_  module1/
|_  module2/
|_  module3/
|_  module4/
|_  module5/
|_  outputs/          # use this for your simulation outputPath
|_  packages/         # project-specific package library
...

Most SpaDES users will get modules via downloadModule(), and should save these modules in the project’s modules/ sub-directory. New modules should also be created in this directory. Remember that each module should be self-contained, and that data are typically stored in the module’s data/ sub-directory (though, see below re: inputs/).

### Filepaths

• use relative file paths within the main project directory

• paths external to the project, such as /tmp and /scratch, may not be globally available, so avoid hardcoding these:

• use per-user and per-machine configurations, or setup symlinks to these location that point to their system-specific locations
• e.g., myProject/scratch --> /scratch/myUser/myProject/
• e.g., use file.path(tempdir(), "myProject") instead of /tmp/myProject to ensure cross-platform availability e.g., on Windows
• do not use getwd() nor setwd() within scripts, modules, etc.

### Project caches (cache/)

• why use cache
• using cache subdirs / separate caches per stage in workflow
• mention using alt cache db backends
• if using git, make sure this directory is listed in .gitignore

### Simulation inputs (inputs/)

• why this preferred over module cache directories (reduce duplication of common data objects)
• if using git, make sure this directory is listed in .gitignore

### Simulation outputs (outputs/)

• specify unique output subdirectory for each run/rep (these are typically scenario-specific)
• if using git, make sure this directory is listed in .gitignore

### Standalone package library (packages/)

• don’t muck with system packages / interfere with other projects
• how to configure:
• using Require
• ‘manually’ via .Rprofile
drat:::add("PredictiveEcology")

if (!require("Require")) {install.packages("Require"); library(Require)}
Require::setup("packages")
Require(c("SpaDES", "SpaDES.experiment", "raster", "LandR", "dplyr", "data.table", "amc"))

## Control scripts

Although individual modules will be doing most of the heavy lifting during simulations, these modules still need to be initialized and parameterized correctly. Smaller projects may simply rely on a single ‘global’ control script (e.g., global.R) to run the simulations. However, larger, more complex, projects benefit from splitting up the workflow across a series of control scripts, which should be sequenced and grouped based on their function. This allows each ‘stage’ of the workflow to e.g., be cached or independently executed. For example, a project directory may contain the following control scripts:

|_ 00-global.R       # the main control script; source()'s the others
|_ 01-init.R         # parameter initialization
|_ 02-paths.R        # define and create paths
|_ 03-packages.R     # load/declare packages used
|_ 04-options.R      # set R and package options
|_ 05-runSim.R       # initialize and run the simulation
|_ 06-postprocessing.R # post-simulation analyses/results summaries
...                    # other scripts

In addition to these R scripts, other scripts (e.g., bash, slurm) may be used to setup batch runs and/or run simulations on HPC clusters.

### Main script

The primary (global, a.k.a. main) script defines the (usually linear) flow of the other scripts and should be kept as clutter-free as possible. The simplest approach to structuring your workflow is to assume the user will run the main script interactively (e.g., line-by-line) or from the command line (e.g., Rscript 00-global.R). In order to facilitate running this global script for use with different simulation scenarios, on different machines, by different users, as well as being able to easily reuse scripts with different, but related projects, it’s important to reduce idiosyncracies in these scripts by putting user-configurable components into separate config or options files. To ensure these can quickly be rerun, it’s critical to stash intermediate results so that long or intensive computations don’t need to be rerun each time.

### Project configuration files

This workflow recognizes that there are frequently different types of configurable projects parameters. - Some are intended to be set by the user for their machine (e.g., scratch path, or number of CPU threads or amount of RAM to use). - Some are set using different values depending on the desired scenario or replicate being run. These may be passed to individual modules, but controlled at the top level of the simulation control scripts. - Some are package- or module-level options that differ from the defaults, or are explicitly being defined to reduce ambiguity and increase transparency (both of which help reduce coding errors, and speed up debugging).

It is useful to try to group these configurable parameters based on when/how they are used in the simulation, and to keep them organized (e.g., alphabetized) so it’s easy to scan the list of parameters and identify their corresponding values. Thus, there are two (or optionally, three) main places where these values may be set (and thus three places where you should check if you are updating/changing parameters or their values).

The first place is in 01-init.R (and optionally, some these values may additionally read in from a config file using e.g., the config package). Parameter values are set here early on and may use those objects later in various places (including e.g., 04-options.R). When running simulations, it’s typical that a user would be running multiple concurrent simulations and would set a configuration value for the first simulation (A), and want to change the value for the next simulation (B). A problem arises where if the first simulation (A) hasn’t gotten far enough along in the scripts to already have read these values into memory, simulation A could read in the updated value from disk intended for simulation B. Thus, all config values coming from a file (being read from disk) need to be read in as early as possible so if the file changes it won’t interfere with in-progress (or queued future) simulations (i.e., reduce race conditions).

To mitigate this, it is useful to encode run information, including key parameter values, in the simulation runName, so that in can be extracted during the simulation. E.g., for runName = "AOU_CCSM4_RCP85_res250_rep01": - AOU specifies the study area (one of AOU or ROF); - CCSM4_RCP85 specifies the climate scenario; - res250 is the pixel resolution; and - rep01 specifies the replicate/run/realization number. Thus, the construction of the runName can be done by a high-level control script rather than having the user manually edit a configuration file, which is especially useful when doing batch runs.

(An alternative approach is to use separate “config” or “param” files for each set of simulations, which for complex projects with multiple defined runs could mean tens or hundreds of nearly identical text files needing to be maintained and updated. Thus, adding a new config option (or removing one) means editing and updating all of those files. Though this approach has other merits, this is a very large drawback.)

As alluded to above, another place where configuration parameters are set is in 04-options.R. This is a single place where all package-level options are set. They should be listed alphabetically, so that it’s easy for a human to read, find, and modify values. Where these values are not hardcoded to a fixed value (e.g., Ncpus = 8L), they should be set using variables defined in 01-init.R (e.g., Ncpus = ncores, where ncores was previously defined as parallel::detectCores() / 2)

#### Replication and scenarios

The simplest way to provide information about replicate or run id, as well as scenarios, is to provide them as part of the simulation run name (as described above).

The run name (and other metadata about the simulation) can also be inserted into the simList as a ‘dot-object’:

objects4sim <-  list(
...,
.runName = runName ## runName is a character string
)

...

mySim <- simInit(..., objects = objects4sim)

Simulation outputs should be saved in run-specific output directories, thus we suggest using runName as part of the simulations’ output path. This also helps the user when browsing the outputs in the filesystem when examining results.

#### Per-user and per-machine config

Lorem ipsum …

• clearly define which 01-init.R vars are ‘global’ and which are intended to be changed by the user
• config package + config.yml?

### Save or cache intermediate results

For each computational ‘stage’ of a project workflow, try to ensure that (at a minimum) intermediate results are saved to a file locally. This can be done using the Cache() mechanisms build provided the reproducible and SpaDES.core packages, and can also involve additional “manual” saving of objects using saveRDS() or qs::qsave(). These objects can be scripted to be loaded on subsequent runs.

To quickly get started with the project on a new machine, one can take advantage of cloud storage provided by Google Drive, and upload/download these saved objects using googledrive::drive_upload() and googledrive::drive_download. Examples of this use are provided in the advanced project template scripts.

## Version control

### Simple module versioning

Every module has a version number in its metadata. To download a specific version of a module via downloadModule(), specify the version argument. This should be included in your project’s main script / Rmd file. Every project should be explicit about which versions of the modules it is using.

### Using git

More advanced users and developers may choose to use more recent or in-development versions of the modules instead of the versions in the SpaDES-modules repository (and accessed via downloadModule()). Many SpaDES module authors/developers use GitHub for version control, so we can get tagged module versions as well as in-development versions of the code. To use version-controlled SpaDES modules in your project, we use git submodules.

Here, we assume that you are familiar with git (and GitHub) and are also using it for version control of your own project.

myProject/            # a version controlled git repo
|_  .git/
|_  cache/            # should be .gitignore'd
|_  inputs/           # should be .gitignore'd (selectively)
|_  manuscripts/
|_  modules/
|_  module1/      # can be a git submodule
|_  module2/      # can be a git submodule
|_  module3/      # can be a git submodule
|_  module4/      # can be a git submodule
|_  module5/      # can be a git submodule
|_  outputs/          # should be .gitignore'd
...

Remember that large data files should not managed using git. Each module’s data directory should have it’s own .gitignore file. These data files should be easily retrieved via download or created by the module. This also means you should add inputs/, outputs/, and cache/ to your project directory’s .gitignore file!

#### Using git submodules

We will add each of the SpaDES modules to our project as git submodules via the command line (but GitKraken does support git submodules). (You’ll need to delete the moduleN/ sub-directories within modules.)

cd ~/Documents/myProject/modules
git push origin master

Now our directory structure looks like this:

myProject/            # (https://github.com/MYUSERNAME/myProject)
|_  .git/
|_  cache/            # should be .gitignore'd
|_  inputs/           # should be .gitignore'd (selectively)
|_  manuscripts/
|_  modules/
|_  module1/      # git submodule (https://github.com/USERNAMEA/module1)
|_  module2/      # git submodule (https://github.com/USERNAMEA/module2)
|_  module3/      # git submodule (https://github.com/USERNAMEB/module3)
|_  module4/      # git submodule (https://github.com/USERNAMEB/module4)
|_  module5/      # git submodule (https://github.com/USERNAMEC/module5)
|_  outputs/          # should be .gitignore'd
...

In the above example, we are working with 6 different GitHub repositories, one for each SpaDES module plus our myProject repo.

Now, we manage each of the SpaDES modules (git submodules) independently. Because each of these submodules simply link back to another git repository, we can make changes upstream in the corresponding repo. We then need to pull in these upstream changes to specific modules as follows:

cd ~/Documents/myProject/modules
git submodule update --remote module1

If we make changes to modules locally and want to push them to the remote we can do so using:

cd ~/Documents/myProject/modules/module1
git push

This will push only the (committed) changes made to module1.

## Parent and child modules

Another option (as a developer) to make working with multiple SpaDES modules easier, is to create a parent module that specifies a group of modules as its children. In this way, a user only needs to call downloadModule() or simInit() specifying the parent module name.

Even though a parent (and grandparent, etc.) module can be thought hierarchically above child modules, remember that from a directory structure standpoint, all modules (child or parent) are at the same level:

myProject/            # a version controlled git repo
|_  .git/
|_  cache/            # should be .gitignore'd
|_  inputs/           # should be .gitignore'd (selectively)
|_  manuscripts/
|_  modules/
|_  parent1/      # with children: modules 1-5
|_  module1/
|_  module2/
|_  module3/
|_  module4/
|_  module5/
|_  outputs/          # should be .gitignore'd
...

Here, all of these modules (including the parent) can be git modules, and thus managed independently.

## Summary

The take away here is that when it comes to basic project organization, use a single directory for the project, and organize SpaDES modules within a single sub-directory therein. If you’re using git version control (and you really should be using version control!) then git submodules offer an elegant way to manage dependencies.

## Other resources

• Using alternative cache backends [link]