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Dataplot: Spikes

Introduction Dataplot can draw a curve as a character or plot symbol at each point, as a connected line, as a spike from the point to a base, as a bar from the point to a base, or as any combination of the above (including drawing none or all of them). The choice is determined by the LINE, CHARACTER, SPIKE, and BAR commands. The switches for these commands work independently of each other.
Description A spike is a vertical line from the plot point to the spike base (often the x axis, but it can be other values such as the mean).

The spike is most often drawn as a solid line, but you can draw it using a dash or dot pattern as well. The available line patterns are the same as for drawing lines.

Some Common Usage Spikes are commonly used in time series plots. They are also useful in showing deviation from a common value such as the mean or median. They are also used to draw dot charts, which are an alternative to bar plots recommended by Bill Cleveland in the book "Elements of Graphing Data".
Use of Short Forms The short designations (e.g., BL for BLANK, SO for SOLID, DA3 for DASH3) allow for the specification of a large number of spike types on a single command line, as in
    SPIKE SO SO SO SO SO DO DO DO DO DO ...
      DA DA DA DA DA
How Dataplot Decides Which Spike Pattern to Use For single-trace plots, as from
    PLOT Y X
Dataplot makes use of the first spike type specified.

For multi-trace plots, as from

    PLOT Y1 Y2 Y3 Y4 Y5 VS X
    PLOT Y X TAG
Dataplot makes use of the respective spike types for each trace; thus the first spike type defines the type for the first trace, the second spike type defines the type for the second trace, and so forth.
Dataplot Program Demonstrating the Attributes of Spikes Dataplot allows you to set the base, line style, thickness, and color of the spike as demonstrated by the following Dataplot program.
    SKIP 25
    READ BOXJE142.DAT YIELD
    .
    TITLE TIME SERIES PLOT
    Y1LABEL YIELD
    X1LABEL SEQUENCE NUMBER
    XLIMITS 0 70
    XTIC OFFSET 2 2
    LET N = SIZE YIELD
    LET A = MEAN YIELD
    CHARACTER OFF
    SPIKE ON
    LINE BLANK
    .
    MULTIPLOT 2 2
    MULTIPLOT CORNER COORDINATES 0 0 100 100
    PLOT YIELD
    .
    SPIKE BASE A
    PLOT YIELD
    LINE SOLID
    DRAWDATA 1 A N A
    LINE BLANK
    .
    SPIKE THICKNESS 0.3
    PLOT YIELD
    LINE SOLID
    DRAWDATA 1 A N A
    LINE BLANK
    .
    SPIKE COLOR BLUE
    LINE SOLID
    LINE COLOR BLUE
    PLOT YIELD
    DRAWDATA 1 A N A
    END OF MULTIPLOT
Dataplot Graph The above program generated the following Dataplot graph.

Plot demonstrating use of spikes in Dataplot

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Date created: 6/5/2001
Last updated: 10/30/2013

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