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DESCRIPTION
proc curvefit fits a curve to the data and renders
the curve with a line.
FEATURES
Can compute moving average, linear regression, or bspline curve.
Also, complete control over color, width, and dash style of line.
EXAMPLES
See the Gallery curvefit examples
PREREQUISITES
A plotting area must be set up using proc areadef
and proc getdata must be executed to
access or define some data.
The data may be presented in any order; proc curvefit will order it in X.
MODES
Like proc lineplot, data may be given for both X and Y
or just for Y. In the latter case, sequential unit locations are
used for the X component.
VARIABLES THAT ARE SET
REGRESSION_LINE
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If curvetype is regression, this variable will be set to display
the formula for the regression line.
CORRELATION
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If curvetype is regression, this variable will be set to display
the Pearson correlation coefficient (r), which ranges from -1.0 to 1.0, where
1.0 is a strong correlation (positive slope), -1.0 is a strong correlation
(negative slope), and 0 is no correlation.
MANDATORY ATTRIBUTE
The yfield attribute MUST be specified.
ATTRIBUTES
yfield
dfield
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Data field to use for Y values.
Example: yfield: 1
xfield
dfield
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Data field to use for X values.
If not given, sequential unit locations in X will be used.
Example: xfield: 4
curvetype movingavg | regression | bspline | avg
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The type of curve fitting computation to perform.
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movingavg: For each point, it takes the average of the current point and n-1
points to the left (or as many points as are available).
n is controlled by the order attribute.
Often used in finance.
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regression computes the linear regression for the set of points. The result will be a
straight line expressing the relationship between X and Y. Often used with scatterplots.
The variables REGRESSION_LINE and CORRELATION will be set (see VARIABLES above).
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bspline draws a curve using the bspline algorithm. The order and resolution
attributes control the appearance of the result. May be used to fit a curve to a histogram.
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avg is similar to movingavg except that it also includes n-1 points to the right
of the current point (or as many points as are available) in the average.
Thus, for a point that is far from either edge, 2n-1 points will be averaged.
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Example: curvetype: movingavg
order n
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For bspline curves, this is a value between 2 and 20; a lower value
yields a more jagged curve, while a higher value gives a smoother curve.
The number of data points must be at least this value for a bspline curve
to be possible.
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For movingavg curves, this defines the number of points
to include in each average computation. For avg curves, 2n - 1
points will be considered, where n = the order value.
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This attribute has no effect with regression curve.
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Default order for either type of curve is 4.
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Example: order: 8
resolution n
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Only relevant for bspline curves.
For every input point, n result points will be generated.
Default is 5.0.
linedetails
linedetails
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Rendering details for the curve.
Example: linedetails: color=red width=2.0 style=2
calcrange min [max]
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Data within this range will be included in curve calculation.
If only one value is given, it will be taken as the range
minima and the maxima will be the plottable maxima.
If not specified all data rows will be included.
linerange min [max]
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Controls the X range (in scaled units) within which the curve will be rendered.
Data points falling outside this range will not be rendered.
If accumulation is being done, points outside the range will contribute
to the accumulated total.
If only one value is given, it will be taken as the range
minima and the maxima will be the plottable maxima.
If not specified all data rows will be plotted.
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For regression curves, this attribute may be used to limit
the X range of the regression line, or to create a regression line that extends
beyond the X range of the data.
In this case, min and max should both be given.
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Example: linerange: 1
legendlabel
text
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A label to be associated with the curve in the legend.
proc legend must be executed later in order to
render the legend.
If
proc getdata field names
are being used,
the special symbol #usefname causes the field name of yfield
to be automatically used as the legend label (new in 2.04).
Example: legendlabel: Northeast region
Example: legendlabel: #usefname
select
conditional-expression
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Allows selected data points to be included in curve computation.
showresults yes | no
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If yes, a listing of the points in the computed curve will
be written to the diagnostic stream (-diag).
statsonly yes | no
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For regression curves, this option may be used if it is desired to
compute the REGRESSION_LINE and CORRELATION variables but display no curve.
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data display engine
Copyright Steve Grubb
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