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help for ^loopplot^
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Scatter plots with loops
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^loopplot^ varlist [weight] [^if^ exp] [^in^ range] [^,^ graph_options]
Description
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^loopplot^ produces a scatter or twoway plot for varlist, in which
^connect(l)^ has the effect of producing a loop: the last data point is
joined to the first. This is achieved by temporarily appending one or more
extra observations to the data set that copy the first relevant non-missing
observation for each loop.
Options
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graph_options are options allowed with ^graph, twoway^, including ^by()^.
^sort^ is allowed but ignored.
Remarks
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There are some known side-effects of appending extra observations:
^sy([_n])^ is marred by overwriting of ^_n^ for the first
observation and its copy. The correct effect can be achieved by
. ^gen id = _n^
. ^loopplot y x, c(l) sy([id])^
There are various small or large effects on other ^connect^ options.
Suppose there are several variables to be plotted on the y axis. Each
variable should define just one loop. (If any variable specifies more
than one loop, there would be spurious connections between them.)
Suppose we have four loops defined by
^y1^ and ^x1^
^y2^ and ^x2^
^y3^ and ^x3^
^y4^ and ^x4^
then to meet the Stata rule that only one variable can be plotted on the
x axis it is necessary to pack the four x variables into one. A
satisfactory data structure to start with is
^y1 . . . x1^
^. y2 . . x2^
^. . y3 . x3^
^. . . y4 x4^
stacked into
^Y1 Y2 Y3 Y4 X^
Here the ^.^ represent blocks of missing values. This data structure
could be produced by using ^stack^, or by direct entry of the data.
Examples
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. ^loopplot rain temp, c(l)^
. ^loopplot rain temp, c(l) by(station)^
Author
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Nicholas J. Cox, University of Durham, U.K.
n.j.cox@@durham.ac.uk
Also see
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On-line: help for @graph@