Here is a rough program that allows
separate jittering. Given #, the sd of the noise
is #/500 of the range on the axis specified,
or #/500 when that variable is a constant.
I made up this criterion and anyone is
at liberty to clone the program and use
their own.
*! NJC 1.0.0 20 January 2006
*! separate jittering of x and y coordinates
*! Example: jscatter mpg rep78, xj(2)
program jscatter
version 9
syntax varlist(min=2 max=2) [if] [in] ///
[, XJitter(numlist max=1 >=0) YJitter(numlist max=1 >=0) *]
marksample touse
qui count if `touse'
if r(N) < 2 error 2001
tokenize `varlist'
args y x
qui if "`xjitter'" != "" {
tempvar xclone
clonevar `xclone' = `x'
if `"`: var label `xclone''"' == "" label var `xclone' "`x'"
su `x' if `touse', meanonly
if r(max) == r(min) {
local range = 1
local xopt "xsc(r(`= r(max) - 0.5' `= r(max) + 0.5'))"
local xopt "`xopt' xla(`= r(max)')"
}
else local range = r(max) - r(min)
replace `xclone' = `xclone' + ///
invnorm(uniform()) * (`xjitter' / 500) * `range'
local x "`xclone'"
}
qui if "`yjitter'" != "" {
tempvar yclone
clonevar `yclone' = `y'
if `"`: var label `yclone''"' == "" label var `yclone' "`x'"
su `y' if `touse', meanonly
if r(max) == r(min) {
local range = 1
local yopt "ysc(r(`= r(max) - 0.5' `= r(max) + 0.5'))"
local yopt "`yopt' yla(`= r(max)')"
}
else local range = r(max) - r(min)
replace `yclone' = `yclone' + ///
invnorm(uniform()) * (`yjitter' / 500) * `range'
local y "`yclone'"
}
scatter `y' `x' if `touse', `xopt' `yopt' `options'
end
Nick
[email protected]
n j cox
> There is no need to write off adding noise yourself
> as a "manual" solution. This should be easily programmable,
> and without action from StataCorp, so why not do that to get
> what you want?
>
> Alternatively, there are other solutions to get a
> neat display of repeated values, by stacking not
> jittering. I have found that jittering often has two disadvantages:
>
> 1. It can be tricky to get exactly what you want, because
> of the randomness.
>
> 2. Lots of people seem not to have heard of jittering, so
> with some audiences you have to go into explanations.
> Stacking needs far less explanation.
>
> Stacking is precisely what -dotplot- does. If you don't like the way
> that -dotplot- offers you control of the binning, then
> -stripplot- from SSC is an alternative.
>
> David Airey
>
> The jitter option in Stata graphs adds user controlled amounts of
> spherical noise to plotted data, useful for categorical data plots to
> prevent overprinting. But when only the X axis of a plot is
> categorical, I don't necessarily want to add scatter in my Y axis. I
> just want to add scatter in the X axis. It would be nice to have the
> jitter option take two arguments, one for X and one for Y, say,
>
> scatter y x, jitter(0 7)
>
> to jitter the x axis only.
>
> I know I can manually add some amount of random noise to a new
> generated variable of X and plot that, but making the jitter option
> do the above would be more desirable for me!
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
