gt1mAccFile: Read a single accelerometer file

In pawacc: Physical Activity with Accelerometers

Description

This function reads an Actigraph GT1M accelerometer file.

Usage

gt1mAccFile(file, path, fileid, counts.pos = 1,
	tz = "Europe/London", sparse = FALSE,
	fault = 32767)

Arguments

file	file name including file extension.
path	path to file.
fileid	label for file identifier.
counts.pos	when storage mode allows for accelerometer counts and steps to be recorded at the same time, this argument specifies the position of first measurement of accelerometer counts (default is counts.pos = 1).
tz	a character string specifying the timezone to be used for the conversion (see strptime).
sparse	logical flag: should data be stored in sparse format?
fault	numerical value that indicates voltage signal saturation.

Details

Raw accelerometer data are processed according to the device data format. Several data checks are performed by errorChk and infoDate. An additional check is performed on the lenght of the sequence of measurements when both accelerometer counts and steps are recorded. If the length is odd, a warning message is produced. See file 'gt1m_sample.dat' in directory '\inst\extdata' of this package.

Value

These functions return an object of two classes: accfile and additional device-specific class (i.e., gt1m).

An object of class accfile is a list containing the following components:

df	A data.frame object with accelerometer values in columns counts and steps (if present), and coded error for each accelerometer data column. See errorChk for error codes. If sparse = TRUE, all variables of the data frame df are returned as vectors of a matrix in sparse format (see as.matrix.csr for details).
info	A data.frame object with file identifier (fileid), device serial number (serial), number of recorded measurements (nobs), epoch (epoch), accelerometer mode (mode), start date and time (ts_start), time zone (tz), battery voltage (voltage), download date and time (ts_dl).
error_summary	A list object with file identifier (fileid), summary tables of error codes for each accelerometer data column, error code for date (date), and logical flag for odd number of measurements (odd_number) (see details).

Author(s)

Marco Geraci

References

Actigraph (Pensacola, Florida).

Geraci M, Rich C, Sera F, Cortina-Borja M, Griffiths LJ, and Dezateux C (2012). Technical report on accelerometry data processing in the Millennium Cohort Study. London, UK: University College London. Available at http://discovery.ucl.ac.uk/1361699

See Also

readAccDir, gt1mAccDir

Examples

data(gt1m_sample)
class(gt1m_sample)

pawacc documentation built on May 2, 2019, 5:12 a.m.