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help for ^gphdt^ (STB-34: gr20)
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Low level graphics in data coordinates
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^gphsave^
^gphdt c^lear y_1 x_1 y_2 x_2
^gphdt t^ext y x #_rotation #_alignment text
^gphdt vt^ext varname_y varname_x varname_str [^if^ exp] [^in^ range]
^gphdt l^ine y_1 x_1 y_2 x_2
^gphdt vl^ine varname_y varname_x [^if^ exp] [^in^ range]
^gphdt vpol^y varname_y_1 varname_x_1 varname_y_2 varname_x_2 ...
varname_y_p varname_x_p [^if^ exp] [^in^ range]
^gphdt b^ox y_1 x_1 y_2 x_2 #_shade
^gphdt p^oint y x #_delta_c #_symbol
^gphdt vpoi^nt varname_y varname_x [varname_delta_c varname_symbol]
[^if^ exp] [^in^ range] [^, size(^#_delta_c^) symbol(^#_symbol^)^]
Description
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In this section we refer to a data coordinate as (x,y) where x and y are the
horizontal and vertical coordinates of the point. In the arguments of the
^gphdt^ commands we have preserved Stata's usual practice of putting the
vertical position first.
^gphdt clear^ y_1 x_1 y_2 x_2 clears the rectangle having opposite corners
(x_1,y_1) and (x_2,y_2).
^gphdt text^ y x #_rotation #_alignment text displays text at data coordinate
(x,y). See ^[R] gph^ for information about the rotation and alignment
arguments.
^gphdt vtext^ varname_y varname_x varname_str [^if^ exp] [^in^ range] displays
N centered lines of horizontal text where the location and text for the
lines are contained in the three variables.
^gphdt line^ y_1 x_1 y_2 x_2 draws a line from data coordinate (x_1,y_1) to
(x_2,y_2).
^gphdt vline^ varname_y varname_x [^if^ exp] [^in^ range] draws a series of
connected lines where the consecutive data coordinates are contained
in the two variables.
^gphdt vpoly^ varname_y_1 varname_x_1 varname_y_2 varname_x_2 ... varname_y_p
varname_x_p [^if^ exp] [^in^ range] draws a series of connected lines for
each observation in the input variables.
^gphdt box^ y_1 x_1 y_2 x_2 #_shade draws a rectangle having opposite corners
having data coordinates (x_1,y_1) and (x_2,y_2). The shading argument must
be between 0 and 5 where the shading gets darker from 0 to 4, and 5 means
there is no shading.
^gphdt point^ y x #_delta_c #_symbol displays a point at data coordinate
(x,y). See ^[R] gph^ for information on the size and symbol arguments.
^gphdt vpoint^ varname_y varname_x [varname_delta_c varname_symbol] [^if^ exp]
[^in^ range] [^, size(^#_delta_c^) symbol(^#_symbol^)^] displays points at
the data coordinates contained in the variables. See ^[R] gph^ for
information on the size and symbol arguments.
Remarks
-------
For the ^gphdt^ commands to work properly, one must call ^gphsave^ immediately
after calling ^graph^. This puts the elements of ^_result(5)^ through ^_result(8)^
into the global macros ^GPH_ay^, ^GPH_by^, ^GPH_ax^, and ^GPH_bx^ for the ^gphdt^
commands to use.
Examples
--------
A standard example of adding graphic components to a plot is to add the least
squares regression line to a scatterplot as well as line segments showing
vertical deviations of observed points to the line. Here is a simple program
called ^slrplot^ for doing this for a given dependent variable ^y^ and
independent variable ^x^. The program uses ^gphdt vpoly^ to draw the line
segments and ^gphdt line^ to draw the regression line.
^program define slrplot^
^version 5.0^
^local y "`1'"^
^local x "`2'"^
^tempvar yhat^
^gph open^
^graph `y' `x', xlab ylab^
^gphsave^
^regress `y' `x'^
^predict `yhat'^
^gphdt vpoly `y' `x' `yhat' `x'^
^sum `x'^
^local x1 = _result(5)^
^local x2 = _result(6)^
^local y1 = _b[_cons] + _b[`x']*`x1'^
^local y2 = _b[_cons] + _b[`x']*`x2'^
^gphdt line `y1' `x1' `y2' `x2'^
^gph close^
^end^
^. slrplot price mpg^
Authors
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H. Joseph Newton
Statistics Department
Texas A&M University
email: jnewton@@stat.tamu.edu
James W. Hardin
Stata Corp.
email: tech@@stata.com
Also see
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STB: gr20 (STB-34)
Manual: ^[R] gph^
On-line: help @gph@