[R] ggplot2, geom_hline and facet_grid

Small Sandy (NHS Greater Glasgow & Clyde) sandy.small at nhs.net
Tue Jan 18 10:46:33 CET 2011


I have a long data set on which I want to do Bland-Altman style plots for each rhythm type
Using ggplot2, when I use geom_hline with facet_grid I get an extra set of empty panels.
I can't get it to do it with the "Diamonds" data supplied with the package so here is a (much abbreviated) example:

> lvexs
   cvd_basestudy ecd_rhythm fixed_time variable_time
1       CBP05J02         AF    30.9000       29.4225
2       CBP05J02         AF    33.1700       32.0350
3       CBP05J02         AF    32.5700       30.2775
4       CBP05J02         AF    32.0550       33.7275
5       CBP05J02      SINUS    30.9175       28.3475
6       CBP05J02      SINUS    30.5725       29.7450
7       CBP05J02      SINUS    33.0000       31.1550
9       CBP05J02      SINUS    31.8350       30.7000
10      CBP05J02      SINUS    34.0450       33.4800
11      CBP05J02      SINUS    31.3975       29.8150
>  qplot((variable_time + fixed_time)/2, variable_time - fixed_time, data=lvexs) + facet_grid(ecd_rhythm ~ .) + geom_hline(yintercept=0)

If I take out the geom_hline I get the plots I would expect.

It doesn't seem to make any difference if I get the mean and difference separately.

Can anyone explain this and tell me how to avoid it (and why does it work with the Diamonds data set?

Any help much appreciated - thanks.


Sandy Small
Clinical Physicist
NHS Forth Valley
NHS Greater Glasgow and Clyde


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