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datafilter - Tool

	Package	utility
	Module	mathematics

Postscript file available

Filtering operations on data arrays

include "image.g"

Constructors

datafilter

Construct a Datafilter tool

Functions

done	Destroy this tool
filter	Filter a data array
medianclip	Median clip a data array

Summary

The Datafilter tool provides some simple filtering operations for Glish arrays.

Here is an example where we create a noisy sinusoid with outliers. First we filter the data; you can see how the median filter removes outliers (as well as compressing the noise). Then we also median clip the original data showing how the outliers are effectively removed.

Example

# Generate Gaussian distribution

- include 'randomnumbers.g'
- n := 500
- r := randomnumbers();
- g := r.normal(0.0, 0.5, n);
- r.done()

# Generate data ; sin wave plus noise

- x := (1:n) / 10 / pi
- y := sin(x) + g
#
- include 'pgplotter.g'
- p0 := pgplotter ()
- p0.plotxy (x, y, title='Sin + noise', plotlines=F)

# Now add some outliers

- ii := 1:n
- for (i in ii[ii%50 == 0]) {
y[i] *:= 20;
}
#
- p1 := pgplotter()
- p1.plotxy (x, y, title='Sin + noise + outliers', plotlines=F)

# Generate Datafilter tool

- include 'datafilter.g'
- df := datafilter();

# Median filter returns filtered data

- y2 := df.filter (y, method='median', width=10)
#
- p2 := pgplotter()
- p2.plotxy (x, y2, title='Median filtered', plotlines=F)

# Median clip returns a Boolean mask

- m := df.medianclip (y, width=10, clip=5)
#
- p3 := pgplotter()
- p3.plotxy (x, y, title='Median clipped', plotlines=F, mask=m)