Here is another approach using transform and ave which I think is a little simpler than the others suggested:
> new.data <- transform( iris, + normSW = Sepal.Width / ave(Sepal.Width, Species, FUN=max), + normSL = Sepal.Length / ave(Sepal.Length, Species, FUN=max) + ) You can adjust it for your data. Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Sandy Small > Sent: Friday, November 09, 2007 3:57 AM > To: r-help@r-project.org > Subject: [R] Normalizing grouped data in a data frame > > Hi > I am a newbie to R but have tried a number of ways in R to do > this and can't find a good solution. (I could do it out of R > in perl or awk but would like to know how to do this in R). > > I have a large data frame 49 variables and 7000 observations > however for simplicity I can express it in the following data frame > > Base, Image, LVEF, ES_Time > A, 1, 4.32, 0.89 > A, 2, 4.98, 0.67 > A, 3, 3.7, 0.5 > A, 3. 4.1, 0.8 > B, 1, 7.4, 0.7 > B, 3, 7.2, 0.8 > B, 4, 7.8, 0.6 > C, 1, 5.6, 1.1 > C, 4, 5.2, 1.3 > C, 5, 5.9, 1.2 > C, 6, 6.1, 1.2 > C, 7. 3.2, 1.1 > > For each value of LVEF and ES_Time I would like to normalise > the value to the maximum for that factor grouped by Base or > Image number, adding an extra column to the data frame with > the normalised value in it. > > So for the Base = B group in the data frame (the data frame > should have the same length I'm just showing the B part) I > would get a modified data frame as follows. > > Base, Image, LVEF, ES_Time, Norm_LVEF, Norm_ES_Time ... > B,1,7.4, 0.7, 7.4/7.8, 0.7/0.8 > B, 3, 7.2, 0.8, 7.2/7.8, 0.8/0.8 > B, 4, 7.8, 0.6, 7.8/7.8, 0.6/0.8 > ... > > Where the results of the division would replace the division > shown here. > I hope this makes sense. > If anyone can help I would be very grateful. > > Sandy Small > NHS Glasgow, UK > > > ********************************************************************** > This message may contain confidential and privileged information. > If you are not the intended recipient please accept our apologies. > Please do not disclose, copy or distribute information in > this e-mail or take any action in reliance on its contents: > to do so is strictly prohibited and may be unlawful. Please > inform us that this message has gone astray before > deleting it. Thank you for your co-operation. > > NHSmail is used daily by over 100,000 staff in the NHS. Over > a million messages are sent every day by the system. To > find out why more and more NHS personnel are switching to > this NHS Connecting for Health system please visit > www.connectingforhealth.nhs.uk/nhsmail > > ______________________________________________ > R-help@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. > ______________________________________________ R-help@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.
