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From |
David Airey <david.airey@Vanderbilt.Edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: weight marker symbol fill size and color? |

Date |
Sun, 24 Aug 2008 13:42:09 -0500 |

.

Great! I get it now, of course. I also read an appreciated Nick Cox's notes to your post. Thanks for taking the time to show how to do this.

Cheers,

-Dave

On Aug 24, 2008, at 1:14 PM, Friedrich Huebler wrote:

Dave,

I asked a similar question on July 29.

http://www.stata.com/statalist/archive/2008-07/msg01081.html

A weighted scatter plot can be combined with markers in different

colors as I learned from Stata tech support. I neglected to share the

solution with the list so let me explain today how this can be done.

The solution involves duplicating the observations and recoding the

group variable in the duplicates. This way the weights are distributed

across all groups.

Say we want to take the census data from your example and identify the

regions with different colors.

. webuse census

. scatter death medage [w=pop65p], msymbol(Oh) name(A)

. twoway (scatter death medage if region==1 [w=pop65p], msymbol(Oh))

(scatter death medage if region==2 [w=pop65p], msymbol(Oh)) (scatter

death medage if region==3 [w=pop65p], msymbol(Oh)) (scatter death

medage if region==4 [w=pop65p], msymbol(Oh)), name(B) legend(off)

I turned off the legend so that it is more easy to see that the

markers in graphs A and B have a different size. Next, expand the data

and set the added observations to missing so that they won't appear in

the graph.

. expand 4

. sort state region

. replace death=. if mod(_n,4) > 0

The next step is to recode the region in the added observations.

. recode region (1=2) (2=3) (3=4) (4=1) if mod(_n,4) == 1

. recode region (1=3) (2=4) (3=1) (4=2) if mod(_n,4) == 2

. recode region (1=4) (2=1) (3=2) (4=3) if mod(_n,4) == 3

Now we can draw a graph in which the markers have the same size as in graph A.

. twoway (scatter death medage if region==1 [w=pop65p], msymbol(Oh))

(scatter death medage if region==2 [w=pop65p], msymbol(Oh)) (scatter

death medage if region==3 [w=pop65p], msymbol(Oh)) (scatter death

medage if region==4 [w=pop65p], msymbol(Oh)), name(C) legend(off)

Below is the solution to the example from my original post of July 29.

. clear all

. input x y weight group

1 1 1 1

2 1 2 1

1 2 4 2

2 2 8 2

end

. scatter y x [w=weight], name(A)

. twoway (scatter y x if group==1 [w=weight]) (scatter y x if group==2

[w=weight]), name(B) legend(off)

. expand 2

. replace x = . if _n>(_N/2)

. recode group (1=2) (2=1) if x==.

. twoway (scatter y x if group==1 [w=weight]) (scatter y x if group==2

[w=weight]), name(C) legend(off)

Friedrich

On Sun, Aug 24, 2008 at 11:42 AM, David Airey

<david.airey@vanderbilt.edu> wrote:

At this page, we see how to change symbol size by using (analytic) weights:

http://www.stata.com/support/faqs/graphics/gph/graphdocs/ scatter5.html

e.g.,

webuse census

scatter death medage [w=pop65p], msymbol(circle_hollow)

Can we change both symbol size and color shading as in the R example below?

-Dave

###------------------create the test data.frame

y = c(.4, 1, 2.15, 1.8, 2.7, 2.2, 1.3, .25, 1.1, .1)

x = c(.35, .4, .41, 1.4, 2.1, 2.25, 2.15, 2.2, 1.45, 1.3)

z = c(9, 7, 7.5, 7.3, 7, 7.1, 7.75, 9.5, 8, 10)

d = data.frame(x = x, y = y, z = z)

d$col = gray(.5)

d$col[d$z>=9] = gray(.2)

d$col[d$z<7.5] = gray(.7)

#thikness = sqrt(d$y^2 + d$x^2)

thikness = abs(d$y) + abs(d$x)

###----------------simple, 2-D plot

plot(d$x, d$y, pch=19, cex=(d$z-min(d$z)/1.5), xlim = c(-1.5,4), ylim =

c(-2.5,5), col=d$col)

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**References**:**st: weight marker symbol fill size and color?***From:*David Airey <david.airey@Vanderbilt.Edu>

**Re: st: weight marker symbol fill size and color?***From:*"Friedrich Huebler" <fhuebler@gmail.com>

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