[R] Calculating SD according to groups of rows

[Simon Blomberg]

How about:

with(dat, tapply(HR, SUBJECT_ID, sd))

Assuming your data frame is named dat.

On Wed, 2008-11-19 at 23:59 -0500, pufftissue pufftissue wrote:
> *Hi all,
> 
> I know this is probably basic, but I have proven to be a slow learner in any
> programming language.   Anyhow,
> how can I calculate the SD for each person in my table?  I have two patients
> in this R data.frame, 7200 and 23955.
> I extracted this from a relational database, but am I better off attempting
> to compute SD in SQL, or is this easily accomplished in R?
> 
> 
> *      SUBJECT_ID  HR
> 1        7200 158
> 2        7200 165
> 3        7200 138
> 4        7200 152
> 5        7200 139
> 6        7200 157
> 7        7200 186
> 8       23955 167
> 9       23955 162
> 10      23955 171
> 11      23955 139
> 12      23955 170
> 13      23955 177
> 14      23955 180
> 15      23955 176
> 16      23955 172
> 17      23955 179
> 18      23955 181
> 19      23955 169
> 20      23955 168
> 21      23955 185
> 22      23955 181
> 23      23955 191
> 24      23955 179
> 25      23955 178
> 26      23955 184
> 27      23955 179
> 28      23955 172
> 29      23955 173
> 30      23955 182
> 31      23955 174
> 
> *
> So, what I would want is a table of 800 patients with a SD for their heart
> rates:
> 
> subject id       Heart Rate SD
> 
> 7200              20 (for example)
> 23955           18 (for example)*
> 
> Thank you!
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
-- 
Simon Blomberg, BSc (Hons), PhD, MAppStat. 
Lecturer and Consultant Statistician 
Faculty of Biological and Chemical Sciences 
The University of Queensland 
St. Lucia Queensland 4072 
Australia
Room 320 Goddard Building (8)
T: +61 7 3365 2506
http://www.uq.edu.au/~uqsblomb
email: S.Blomberg1_at_uq.edu.au

Policies:
1.  I will NOT analyse your data for you.
2.  Your deadline is your problem.

The combination of some data and an aching desire for 
an answer does not ensure that a reasonable answer can 
be extracted from a given body of data. - John Tukey.