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Re: st: Force x-axis range to be the bounds of the variable in the sample, not the entire data set


From   Friedrich Huebler <fhuebler@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Force x-axis range to be the bounds of the variable in the sample, not the entire data set
Date   Mon, 27 Aug 2012 13:02:28 -0400

Aaron,

You can automate the range and labels of the x-axis. For example, if
you want the x-axis to have a range of 1.3 to 1.5, with labels at
steps of 0.1, you can do the following.

. sum lnox if _n <= 100
. local xmin = floor(r(min)*10)/10
. local xmax = ceil(r(max)*10)/10
. scatter lprice lnox, xscale(r(`xmin' `xmax')) xlabel(`xmin'(.1)`xmax')

Friedrich

On Mon, Aug 27, 2012 at 12:05 PM, Aaron Kirkman <ak5791@gmail.com> wrote:
> I'm calculating and generating prediction intervals for a subset of a
> data set, but when I graph the subset, the range on the x-axis is the
> range of all of the data, instead of only the sample. For example:
>
> ###
>
> use "http://www.stata-press.com/data/imeus/hprice2a";, clear
> sort lnox
>
> summ lnox
> summ lnox if _n <= 100
>
> ###
>
> . summ lnox
>
>     Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>         lnox |       506    1.693091    .2014102   1.348073   2.164472
>
> . summ lnox if _n <= 100
>
>     Variable |       Obs        Mean    Std. Dev.       Min        Max
> -------------+--------------------------------------------------------
>         lnox |       100    1.435845    .0361544   1.348073    1.48614
>
> The range of the sample is [1.348073, .48614], but when I calculate
> and graph the predicted values, the range of -lnox- is [1.348073,
> 2.164472], which is too large. Here is the complete do-file:
>
> ###
>
> use "http://www.stata-press.com/data/imeus/hprice2a";, clear
> sort lnox
>
> summ lnox
> summ lnox if _n <= 100
>
> quietly regress lprice lnox if _n <= 100
> predict double xb if e(sample)
> predict double stdpred if e(sample), stdp
> scalar tval = invttail(e(df_r), 0.975)
> gen double uplim = xb + tval * stdpred
> gen double lowlim = xb - tval * stdpred
>
> summ lnox if e(sample), meanonly
> local lnoxbar = r(mean)
> label var xb "Predicted"
> label var uplim "95% prediction interval"
> label var lowlim "95% prediction interval"
>
> #delimit ;
>
> twoway
> (rarea lowlim uplim lnox, sort bcolor(gs14))
> (scatter lprice lnox if e(sample), sort ms(Oh) xline(`lnoxbar'))
> (rline uplim lowlim lnox if e(sample), sort),
>                 ytitle("Actual and predicted log price") legend(cols(1))
>                 xsize(18) ysize(12);
>
> #delimit cr
>
> ###
>
> Is there a way to automatically do this, or should I manually specify
> -xaxis- and -xlabel- ?
>
> Thank you,
> Aaron
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