header_table: Header Table
In EGM: Evaluating Cardiac Electrophysiology Signals

header_table

R Documentation

Header Table

Description

header_table() modifies the data.table class to work with header data. The header data is read in from a similar format as to that of WFDB files and should be compatible/interchangeable when writing out to disk. The details extensively cover the type of data that is input. Generally, this function is called by ⁠read_*_header()⁠ functions and will generally not be called by the end-user.

Usage

header_table(
  record_name = character(),
  number_of_channels = integer(),
  frequency = 250,
  samples = integer(),
  start_time = strptime(Sys.time(), "%Y-%m-%d %H:%M:%OSn"),
  ADC_saturation = integer(),
  file_name = character(),
  storage_format = 16L,
  ADC_gain = 200L,
  ADC_baseline = ADC_zero,
  ADC_units = "mV",
  ADC_resolution = 12L,
  ADC_zero = 0L,
  initial_value = ADC_zero,
  checksum = 0L,
  blocksize = 0L,
  label = character(),
  info_strings = list(),
  additional_gain = 1,
  low_pass = integer(),
  high_pass = integer(),
  color = "#000000",
  scale = integer()
)

is_header_table(x)

Arguments

`record_name`	A `character` vector of record line information
`number_of_channels`	An `integer` describing number of signals
`frequency`	A `numeric` value of sampling frequency, 250 Hz default
`samples`	An `integer` for the number of samples
`start_time`	The `POSIXct` time of recording, with miliseconds included. For example, `strptime(start_time, "%Y-%m-%d %H:%M%:%OSn")` where as described in `base::strptime()`
`ADC_saturation`	An `integer` representing ADC saturation
`file_name`	A `character` for the signal specific information
`storage_format`	An `integer` of the bits for the storage format, 16-bit default
`ADC_gain`	An `integer` of ADC gain, default of 200
`ADC_baseline`	An `integer` of ADC baseline, defaults to ADC_zero
`ADC_units`	A `character` to describe ADC units, "mV" is default
`ADC_resolution`	An `integer` for ADC resolution, default is 12
`ADC_zero`	An `integer` for ADC zero, defaults to 0
`initial_value`	An `integer` for the initial value, defaults to ADC_zero value
`checksum`	An `integer` that serves as the checksum
`blocksize`	An `integer` of the block size
`label`	A `character` description of the signal
`info_strings`	A `list` of strings that will be written as an appendix to the header file, usually containing information about the channels, (e.g. list of colors, extra labels, etc).
`additional_gain`	A `numeric` Additional gain, defaults to 1.0
`low_pass`	An `integer` Low pass filter
`high_pass`	An `integer` High pass filter
`color`	A `character` Color as hexadecimal format, defaults to black
`scale`	An `integer` Scale
`x`	A `data.table` object that serves as the header table

Details

The header_table object is relatively complex in that it directly deals with properties of the signal, and allows compatibility with WFDB files and other raw header files for other signal objects. It can be written out using write_wfdb().

Value

A header_table object that is an extension of the data.table class. This contains an adaptation of the function arguments, allowing for compatibility with the WFDB class.

Header file structure

There are three components to the header file:

Record line that contains the following information, in the order documented, however pieces may be missing based on different parameters. From left to right...
- Record name
- Number of signals: represents number of segments/channels
- Sampling frequency (optional)
- Number of samples (optional)
- Time: in HH:MM:SS format (optional)
- Date: in DD/MM/YYYY (optional)
Signal specification lines contains specifications for individual signals, and there must be as many signal lines as there are reported by the above record line. From left to right....
- File name: usually *.dat
- Format integer: represents storage type, e.g. 8-bit or 16-bit
- ADC gain: ADC units per physical unit (optional)
  - Baseline: corresponds to 0 physical units, sep = '*(0)" (optional)
  - Units: with '/' as a field separator e.g '*/mV' (optional)
- ADC resolution integer: bits, usually 8 or 16 (optional)
- ADC zero: represents middle of ADC input range (optional)
- Initial value (optional)
- Checksum (optional)
- Block size (optional)
- Description: text or label information (optional)
Info strings are unstructured lines that contains information about the record. Usually are descriptive. Starts with initial '#' without preceding white space at beginning of line.