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Manual Reference Pages  - STATS (1)

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NAME

stats - calculate some statistics.

CONTENTS

Syntax
Description
Options
Copyright

stats [options] [file]

Calculate statistics for given frames of each input file and write the results on the stdout. If no filenames are given, one input file is expected on the stdin. Otherwise each given filename is processed in turn.

1. frame, width, samplerate

The ‘frame’ option selects a sequence of contiguous frames for processing by:

        frame=a[-b]

where ‘a’ and ‘b’ are frame numbers: 1,2,3,...,max The upper limit ‘b’ is optional, and when it is missing then the frame sequence is a single frame, otherwise ‘a’ and ‘b’ are inclusive limits. The strings "min" and "max" are recognised as extreme limits. Each frame has size ‘width’ samples which may be given with time units (s or ms), in which case the they are converted to a number of samples using the given ‘samplerate’ option. The special option value "width=max" is interpreted as a single frame covering the whole file.

2. type

Datatype for both input and output. Binary types are char, short, int, float, double. Ascii input (one number per line) is recognised with "type=ascii".

3. stat

The statistics available to the ‘stat’ option are:

    n           sample (ie. data set) size
    sum         area
    ss          sum of squares
    mean        sum/n
    rms         root mean square: square root of ss/n
    variance    computed with n-1 degrees of freedom
    stddev      standard deviation: square root of variance
    min         minimum value
    max         maximum value
    absmax      maximum absolute value, ie. max( |max|, |min| )
    range       max-min

The variance is the average squared deviation from the mean value, where the average is computed by dividing by n-1 for a data set of n samples. The stddev is the square root of this variance. The stddev would be equal to the rms value for a data set with zero mean, except that the average squared value is computed using ss/n, while the average squared deviation from a zero mean value is computed using ss/(n-1).

Statistics may be given in a comma separated list, for example:

        stats stat=mean,variance,min,max

For each frame of each input file this will output the four statistics in the data type selected by the ‘type’ option.

4. line

When line=on (or -l) output is forced to be ascii irrespective of the ‘type’ option, and for each file argument in turn stats prints the statistics requested, in the order they were requested, on one line. This makes a table (one line per file), and also helps subsequent operations between statistics. For example, the standard error of the mean (the stddev divided by the square root of the sample size) can be computed:

        stats -l stat=stddev,n  |  awk ’{ print $1 / sqrt($2) }’

Tables can be formatted using field-width and precision arguments which are included as silent options. For example, to format columns with a precision of 4 decimal places with each number right-justified in a field-width of 12 characters:

        stats -l fieldwidth=12 precision=4

The columns may be left-justified by making the fieldwidth parameter negative. Output is truncated to integers by setting the precision parameter 0. For example, to print the sample size of each file as an integer without setting in a field:

        stats -l fieldwidth=0 precision=0  stat=n  [files]

options

Copyright (c) Applied Psychology Unit, Medical Research Council, 1995

Permission to use, copy, modify, and distribute this software without fee is hereby granted for research purposes, provided that this copyright notice appears in all copies and in all supporting documentation, and that the software is not redistributed for any fee (except for a nominal shipping charge). Anyone wanting to incorporate all or part of this software in a commercial product must obtain a license from the Medical Research Council.

The MRC makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.