wrsamp - write WFDB signal files
wrsamp [ options ... ] [ column
... ]
wrsamp reads text-format input and writes the specified columns
in WFDB signal file format 16 (see signal(5)
), either to the standard output
or to a disk file (see the -o option below). If no columns are specified,
all columns are written (but see the -z option below).
Normally, wrsamp’s
input is line- and column-oriented, with line separator characters (usually
ASCII linefeeds) separating input lines, and field separator characters
(usually tabs, spaces, or commas) separating columns within each line.
Columns need not be of constant width; the only requirement is that one
or more field separator characters appear between adjacent columns. The
output of rdsamp(1)
is an example of an acceptable input format, as is
CSV (comma-separated value) format.
If the first input line contains any
alphabetic character, it is assumed to contain signal names (column headings),
and these are copied to the output header file (see the -o option below).
In this case, if the second input line also contains any alphabetic character,
it is assumed to contain unit names (i.e., the names of the physical units
of each signal), and these are also copied to the output header file. Spaces
embedded within unit names are written as underscores in the header file.
Lines are identified by line number. The first line of input not containing
any alphabetic character is line 0. Similarly, columns are identified by
column number, and the leftmost column is column 0. Columns may be selected
in any order, and any given column may be selected more than once, or omitted.
The order of column arguments determines the order of the signals in the
output (data from the first column specified are written as signal 0, etc.)
If an entry in a specified column is "-" (i.e., flagged as missing or invalid),
or if an entry in a specified column is any other non-numeric value, wrsamp
records it as an invalid sample in its output.
If line 0 appears to begin
with a timestamp (a field of the form [hh:mm:ss.sss dd/mm/yyyy]), wrsamp
records it as the base time (starting time) in the output header file.
Options
include:
- -c
- Check that each input line contains the same number of fields.
(This test is normally disabled, to allow for input files containing preambles,
trailers, or occasional extra fields not intended to be read as samples.)
- -d
- Dither the input before converting it to integer output, by adding a
random value to each sample. The random values are selected from a triangular
probability density function between -1 and +1. Dithering is appropriate
whenever the output has a lower resolution than the input. Note that the
RNG used to generate the pseudo-random values is started with a fixed seed,
so that wrsamp’s output is strictly reproducible. Change the seed in the
source and recompile to obtain a different realization of dither if desired.
- -f n
- Start copying with line n. By default, wrsamp starts at the beginning
of its standard input (line 0).
- -F n
- Specify the sampling frequency (in samples
per second per signal) for the output signals (default: 250). This option
is useful only in conjunction with -o, since it affects the output header
file only. This option has no effect on the output signal file, which contains
one sample per signal for each line of input. If you wish to change the
sampling frequency in the signal file, see xform(1)
.
- -G n
- Specify the gain
(in A/D units per millivolt) for the output signals (default: 200). To
specify different gains for each output signal, provide a quoted list of
values in place of n (see the examples below). This option is useful only
in conjunction with -o, since it affects the output header file only. This
option has no effect on the output signal file. If you wish to rescale
samples in the signal file, use -x.
- -h
- Print a usage summary.
- -i file
- Read input
from the specified file (default: standard input).
- -l n
- Read up to n characters
in each line (default: 1024). Longer lines are truncated (with a warning
message identifying the line number of the offending line).
- -o record Write
the signal file in the current directory
- as record.dat, and create a header
file in the current directory for the specified record. By default, wrsamp
writes the signal file to its standard output, and does not create a header
file.
- -O format
- Write the signal file in the specified format (default: 16).
See signal(5)
for descriptions and names of available formats.
- -r c
- Interpret
c as the input line separator (default: \n, the ASCII linefeed character).
This option may be useful, for example, to read Macintosh files containing
carriage-return delimited lines. Note that no special treatment is required
for files containing both carriage returns and linefeeds.
- -s c
- Interpret
c as the input field separator (default: both spaces and tabs are treated
as input field separators). If this option is used, c is the only character
treated as a field separator.
- -t n
- Stop copying at line n (line n is not
processed). By default, wrsamp stops when it reaches the end of file on
its standard input.
- -x n
- Multiply all input samples by n (default: 1) before
writing them to the output signal file. To specify different scaling factors
for each signal, provide a quoted list of values in place of n (see the
examples below).
- -z
- Don’t copy column 0 unless explicitly specified.
It
may be necessary to set and export the shell variable WFDB (see setwfdb(1)
).
rdsamp -r 100s | wrsamp -o 100w -F 360 1 2
This command creates a record named ‘100w’ that is a copy of record ‘100s’
(although the signal file format is different). If the -F 360 option were
omitted, the output signal file (‘100w.dat’) would be unchanged, but the header
file for record ‘100w’ would indicate that the sampling frequency was (the
default) 250 Hz, rather than 360 Hz as in record 100s; this is because
wrsamp has no other way of determining the sampling frequency of its input.
Note that columns 1 and 2 of wrsamp’s input correspond to signals 0 and
1 respectively; column 0 is the sample number, not useful to wrsamp.
wrsamp -i in.txt -o out -G "100 100 50" -x "1 .5 -10 2" 4 1 0 3
This command creates a record named ‘out’ that contains signals derived from
four columns of its input (‘in.txt’). Notice that the argument of the -G (gain)
option is the quoted string "100 100 50"; the effect is that the gains
of the first two output signals are set to 100, and that of the third is
50. Since no explicit gain is specified for the fourth signal, it is assigned
the same gain as the previous (third) signal (i.e., 50). Similarly, the quoted
argument of the -x option specifies scaling factors applied to the samples
before they are written to the output signal file: output signal 0 will
be unscaled (scale factor 1), signal 1 will be halved (.5), signal 2 will
be scaled by 10 and inverted (-10), and signal 3 will be doubled (2)
. Finally,
note that the four columns selected from the input file have been rearranged,
so that the leftmost column (0) will become output signal 2, etc.
rdsamp(1)
,
setwfdb(1)
, xform(1)
, signal(5)
George B. Moody (george@mit.edu)
http://www.physionet.org/physiotools/wfdb/app/wrsamp.c
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