Re: [R] Calculating SD according to groups of rows

From: Simon Blomberg <s.blomberg1_at_uq.edu.au>
Date: Thu, 20 Nov 2008 15:17:50 +1000

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]]
>
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-- 
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.

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Received on Thu 20 Nov 2008 - 05:21:37 GMT

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