# 2. The GGIR pipeline

## The GGIR function

GGIR comes with a large number of functions and optional settings (function arguments also referred to as parameters) that together form a processing pipeline. To ease interacting with GGIR, it has one function to act as interface to all functionality, and this function is also named `GGIR`. You only need to learn how to work with this central function, but it is important to understand that this function interacts with all other functions in GGIR.

Further, it is important to understand that the `GGIR package` is structured in two complementary ways:

- Parts to reflect computational order.
- Parameter themes to reflect functional components.

### Parts of the pipeline

GGIR, has a computational structure of six parts which are applied sequentially to the data:

- Part 1: Loads the data and stores derived signal features or also known as metrics as needed for the following parts.
- Part 2: Basic data quality assessment and description per day and per file.
- Part 3: Estimation of sustained inactivity bouts (rest periods) and sleep, needed for input to Part 4.
- Part 4: Labels the sustained inactive periods derived in Part 3 as sleep, or daytime sustained inactivity, per night and per file.
- Part 5: Compiles time series with classification of sleep and physical activity intensity categories by re-using information derived in part 2, 3 and 4. Next, Part 5 generates a describe summary such as total time in intensity categories, the number of bouts, time spent in bouts and average acceleration per category, and fragmentation.
- Part 6: Facilitates analyses that rely on direct access to the full recording such as household co-analysis and circadian rhythm analysis. The reason why it split up in parts is that it avoids having the re-run all preceding parts if you only want to make a small change in the more downstream parts. The specific order and content of the parts has grown for historical with Part 1 and 2 created in 2011-2013, Part 3 and 4 created in 2013-2015, Part 5 created in 2017-2020, and Part 6 created in 2023-2024.

#### Milestone data

Each part when run stores its intermediate data, which we refer to as the milestone data, in an `.RData` file. This `.RData` file is then read by the next part. Therefore, there is no direct interaction between the parts, all exchange of information works via the `.RData` files. The advantage of this design is that it offers internal modularity to ease re-processing and code development.

The `.RData` files are stored in sub-folders of the output folder:

- Part 1: `meta/basic`
- Part 2: `meta/ms2.out`
- Part 3: `meta/ms3.out`
- Part 4: `meta/ms4.out`
- Part 5: `meta/ms5.out`
- Part 6: `meta/ms6.out`

As user, you are unlikely to ever need to interact with these milestone data because all relevant output for you is stored in csv and pdf files in the output folder `results`. However, it can be useful to know where the milestone data are stored for the following reasons:

- By copying these `.RData` files to a new computer, you may continue your analyses without access to the original data files. This can for example be helpful if you process subsets of the same study on different computers, pooling the resulting milestone data allows you to finalise your analysis on a single computer.
- When you run into a problem, these `.RData` files may allow you to share the problem as a reproducible example of the problem without having to share the original data file.

### Parameter themes

The arguments of all GGIR package functions can be used as input argument to the GGIR function. We will refer to these arguments as input parameters in this documentation. The parameters are structured thematically, independently of the five parts they are used in:

- params_rawdata: parameters related to handling the raw data such as resampling or calibrating.
- params_metrics: parameters related to aggregating the raw data to epoch level summary metrics.
- params_sleep: parameters related to sleep detection.
- params_physact: parameters related to physical activity.
- params_247: parameters related to 24/7 behaviours that do not fall into the typical sleep or physical activity research category.
- params_output: parameters relating to how and whether output is stored.
- params_general: general parameters not covered by any of the above categories

There are a couple of ways to inspect the parameters in each parameter category and their default values:

#### GGIR function documentation:

    ?GGIR

Or visit the .pdf manual and search for function `GGIR`.

#### Parameters vignette:

Documentation for all parameters in the parameter objects can be found the vignette: GGIR configuration parameters.

#### From R command line:

    library(GGIR)
    print(load_params())

If you are only interested in one specific category like sleep:

    library(GGIR)
    print(load_params()$params_sleep)

If you are only interested in parameter `HASIB.algo` from the

`sleep_params` object:

    library(GGIR)
    print(load_params()$params_sleep[["HASIB.algo"]])

All of these parameters are accepted as parameter to function `GGIR`, because `GGIR` is a shell around all GGIR functionality. However, the `params_` objects themselves cannot be provided as input to `GGIR`.

#### Configuration file.

GGIR stores all the parameter values as used in a csv-file named config.csv. The file is stored after each run of GGIR in the root of the output folder overwriting any existing config.csv file. So, if you would like to add annotations in the file, e.g. in the fourth column, then you will need to store it somewhere outside the output folder and explicitly specify the path with parameter `configfile`. Further, the config.csv file itself is accepted as input to `GGIR` with parameter `configfile` to replace the specification of all the parameters, except `datadir` and `outputdir`, see example below.

    library(GGIR)
    GGIR(datadir = "C:/mystudy/mydata",
         outputdir = "D:/myresults",
         configfile = "D:/myconfigfiles/config.csv")

The practical value of this is that it eases the replication of analysis, because instead of having to share you R script with colleagues, sharing your config.csv file will be sufficient.

#### Parameter extraction order

If parameters are provided in the GGIR call, then it always uses those. If parameters are not provided in the function call, GGIR checks whether there is a config.csv file either in the output folder or specified via parameter `configfile` and loads those values. If a parameter is neither specified in the GGIR function call and not available in the config.csv file then GGIR uses its default values which can be inspected as discussed in the section above. Here, it is important to realise that a consequence of this logic is that GGIR will not revert to its default parameter values in a repeated analysis unless you remove the parameter from the function call and delete the config.csv file.

To ensure this is clear here are some example:

- If GGIR is used for the first time without specifying parameter `mvpathreshold` then it will use the default value, which is 100.
- If you specify `mvpathreshold = 120` then GGIR will use this instead and store it in the config.csv file.
- If you run GGIR again but this time delete `mvpathreshold = 120` from your GGIR call then GGIR will fall back on the value 120 as now stored in the config.csv file.
- If you delete the config.csv file and run GGIR again then the value 100 will be used again.

## Input files

### Raw data

1. GGIR currently works with the following accelerometer brands and formats:

- GENEActiv .bin
- Axivity AX3 and AX6 .cwa
- ActiGraph .csv and .gt3x (.gt3x only the newer format generated with firmware versions above 2.5.0. Serial numbers that start with “NEO” or “MRA” and have firmware version of 2.5.0 or earlier use an older format of the .gt3x file). If you want to work with .csv exports via the commercial ActiLife software then note that you have the option to export data with timestamps, which should be turned off. To cope with the absence of timestamps GGIR will calculate timestamps from the sample frequency, the start time and start date as presented in the file header.
- Movisens with data stored in folders.
- Any other accelerometer brand that generates csv output, see documentation for functions `read.myacc.csv` and parameter `rmc.noise` in the vignette Reading csv files with raw data in GGIR.

### Externally derived epoch-level data

By default GGIR assumes that the data is raw as discussed at the start of this chapter. However, for some studies raw data is not available and all we have is an epoch level aggregate. For example, done by external software or done inside the accelerometer device. Although this can introduce some severe limitations to the transparency and flexibility of our analysis, GGIR makes an attempt to facilitate the analysis of these aggregations of the raw data. Please find below an overview of the file format currently facilitated:

Note: For Actiwatch and ActiGraph, physical activity description and sleep classification needs to be tailored to count-specific algorithms: `do.neishabouricounts = TRUE`, `acc.metric = "NeishabouriCount_x"`, `HASPT.algo = "NotWorn"` `HASIB.algo = "NotWorn"`; Note 2: For UK Biobank csv epoch data GGIR does not facilitate sleep analysis as arm angle is not exported.
Sensor brand | Data format | Combine with parameter
--- | --- | ---
Actiwatch | .csv | `dataFormat = "actiwatch_csv"` `extEpochData_timeformat = "%m/%d/%Y %H:%M:%S"`
Actiwatch | .awd | `dataFormat = "actiwatch_awd"` `extEpochData_timeformat = "%m/%d/%Y %H:%M:%S"`
ActiGraph | .csv (count files, not be confused with csv raw data files) | `dataFormat = "actigraph_csv"` `extEpochData_timeformat = "%m/%d/%Y %H:%M:%S"`
Axivity | UKBiobank csv export of epoch level data | `dataFormat = "ukbiobank_csv"`

To process these files GGIR loads their content and saves it as GGIR part 1 milestone data, essentially fooling the rest of GGIR to think that GGIR part 1 created the data. As will be discussed in chapter 2, GGIR does non-wear detection in two steps: The first step is done in part 1 and the second step is done in part 2. In relation to externally derived epoch data non-wear is detected by looking for consecutive zeros of one hour (Actiwatch, ActiGraph) or derived from the file (UK Biobank csv).

2. All accelerometer data that need to be analysed should be stored in one folder or subfolders of that folder. Make sure the folder does not contain any files that are not accelerometer data.
3. Choose an appropriate name for the folder, preferable with a reference to the study or project it is related to rather than just ‘data’, because the name of this folder will be used as an identifier of the dataset and integrated in the name of the output folder GGIR creates.

## How to run your analysis?

The bare minimum input needed for `GGIR` is:

    library(GGIR)
    GGIR(datadir = "C:/mystudy/mydata",
         outputdir = "D:/myresults")

Argument `datadir` allows you to specify where you have stored your accelerometer data and `outputdir` allows you to specify where you would like the output of the analyses to be stored. This cannot be equal to `datadir`. If you copy paste the above code to a new R script (file ending with .R) and Source it in R(Studio) then the dataset will be processed and the output will be stored in the specified output directory.

Next, we can add argument `mode` to tell GGIR which part(s) to run, e.g. `mode = 1:5` tells GGIR to run all five parts and is the default. With argument `overwrite` we can tell GGIR whether to overwrite previously produced milestone data.

Further, argument `idloc` tells GGIR where to find the participant ID. The default setting most likely does not work for most data formats, by which it is important that you tailor the value of this argument to your study setting.

GGIR stores some of its output csv file format with by default comma as column separator. However, this can be modified by argument `sep_reports`.

Each chapter in this digital book will highlight the key arguments related to specific topics.

### From the R console on your own desktop/laptop

Create an R-script and put the GGIR call in it. Next, you can source the R-script with the `source` button in RStudio: `source("pathtoscript/myshellscript.R")`

GGIR by default support multi-thread processing which is used to process one input file per process, which can be turned off by setting parameter `do.parallel = FALSE`.

### In a cluster

If processing data with GGIR on your desktop/laptop is not fast enough then we advise using a GGIR on a computing cluster. The way we did it on a Sun Grid Engine cluster is shown below, please note that some of these commands are specific to the computing cluster you are working on. Please consult your local cluster specialist to explore how to run GGIR on your cluster. Here, we only share how we did it. We had three files for the SGE setting:

submit.sh

    for i in {1..707}; do
        n=1
        s=$(($(($n * $[$i-1]))+1))
        e=$(($i * $n))
        qsub /home/nvhv/WORKING_DATA/bashscripts/run-mainscript.sh $s $e
    done

run-mainscript.sh

    #! /bin/bash
    #$ -cwd -V
    #$ -l h_vmem=12G
    /usr/bin/R --vanilla --args f0=$1 f1=$2 < /home/nvhv/WORKING_DATA/test/myshellscript.R

myshellscript.R

    options(echo=TRUE)
    args = commandArgs(TRUE)
    if(length(args) > 0) {
      for (i in 1:length(args)) {
        eval(parse(text = args[[i]]))
      }
    }
    GGIR(f0=f0,f1=f1,...)

You will need to update the `...` in the last line with the parameters you used for `GGIR`. Note that `f0=f0,f1=f1` is essential for this to work. The values of `f0` and `f1` are passed on from the bash script. Once this is all setup you will need to call `bash submit.sh` from the command line. With the help of computing clusters GGIR has successfully been run on some of the world’s largest accelerometer data sets such as UK Biobank and German NAKO study.

## Processing time

The time to process a typical seven-day recording should be anywhere in between 3 and 10 minutes depending on the sample frequency of the recording, the sensor brand, data format, the exact configuration of GGIR, and the specifications of your computer. If you are observing processing times of 20 minutes or longer for a seven-day recording then probably you are slowed down by other factors.

Some tips on how you may be able to address this:

- Make sure the data you process is on the same machine as where GGIR is run. Processing data located somewhere else on a computer network can substantially slow down software.
- Make sure your machine has 8GB or more RAM memory, using GGIR on old machines with only 4GB is known to be slow. However, total memory is not the only bottle neck, also consider the number of processes (threads) your CPU can run relative to the amount of memory. Ending up with 2GB per process seems a good target. It can be helpful to turn off parallel processing with `do.paralllel = FALSE`.
- Avoid doing other computational activities with your machine while running GGIR. For example, if you use DropBox or OneDrive make sure they do not sync while you are running GGIR. When using GGIR to process large datasets it is probably best not to use the machine. Make sure the machine is configured not to automatically turn off after X hours as that would terminate GGIR. Further, you may like to configure the machine to not fall asleep as that would pause GGIR.
- Reduce the amount of data GGIR loads in memory with parameter `chunksize`, which can be useful on machines with limited memory or when processing many files in parallel. A `chunksize` value of 0.2 (minimum) will make GGIR load the data in chunks of only 20% of the size relative to the chunks it loads by default which is approximately 12 hours of data for the auto-calibration routine and 24 hours of data for the calculation of signal metrics.

## GGIR output

GGIR always creates an output folder in the location as specified with parameter `outputdir`. The output folder name is constructed as `output_` followed by the name of the dataset which is derived from the most distal folder name of the data directory as specified with `datadir`. We recommend this approach because it ensures that output folder name and data directory have matching names. However, it is possible to use `datadir` to specify a vector with paths to individual files, which may helpful if you want to process a set of files but are not in a position to move them to a new folder. In that scenario you will need to set parameter `studyname` to tell GGIR what the dataset name is.

Inside the output folder GGIR will create two subfolders: `meta` and `results` as discussed earlier in this chapter. Inside `results` you will find folder named `QC` (Quality Checks). The name QC (Quality Checks) is possibly somewhat confusing. Data quality checks are best started with the files stored in the results folder, where the files in the QC subfolder offer complementary information to help with the quality check.

GGIR generates reports in the parts 2, 4, 5, and 6 of the pipeline. With parameter `do.report` you can specify for which of these parts you want the reports to be generated. For example, `do.report = c(2, 5)` will only generated the report for parts 2 and 5. For a full GGIR analyses we expect at least the following output files:

Output files in results subfolder:

A detailed discussion of each output can be found in the other chapters.
File path | Resolution | GGIR part
--- | --- | ---
part2_summary.csv | one row per recording | 2
part2_daysummary.csv | one row per day | 2
part4_summary_sleep_cleaned.csv | one row per recording | 4
part4_nightsummary_sleep_cleaned.csv | one row per night | 4
visualisation_sleep.pdf | 40 recordings per page | 4
part5_daysummary_WW_L40M100V400_T5A5.csv | one row per day | 5
part5_personsummary_WW_L40M100V400_T5A5.csv | one row per recording | 5

Output files in results/QC subfolder:

A detailed discussion of each output can be found in the other chapters.
File path | Resolution | GGIR part
--- | --- | ---
data_quality_report.csv | one row per recording | 5
part4_summary_sleep_full.csv | one row per recording | 4
part4_nightsummary_sleep_full.csv | one row per night | 4
part5_daysummary_full_WW_L40M100V400_T5A5.csv | one row per day | 5
plots_to_check_data_quality_1.pdf | one recording per page | 2

Output files in meta/ms5.outraw subfolder:

A detailed discussion of each output can be found in the other chapters.
File path | Resolution | GGIR part
--- | --- | ---
40_100_400/ | one file with time series per recording |
behavioralcodes2023-11-06.csv | dictionary for behavioural codes as used in the time series file |