> 1) I have a dataframe. Based on “formulation” and “subject”, a > dataframe is split into 4 dataframes. The > example is as follows. Moreover, I want > to calculate “test” value for these 4 dataframes. My question is > that the “test” values not > correct and I do not know where the problem is. What does the variable "test" represent? It isn't clear from your code what it means. (Currently it looks like a cumulative rate of change of concentration with respect to time; are you really sure you want this?)
> 2) There are 12 “test” (y) values from 1). Then, I want to model > the relationship > between “concentration” (X) and “test” (Y) by fitting the linear regression, > such lm(Y~X) and this is my target. I > think that if I can catch “test” (Y) values and “concentration” (X) > values into > a dataframe, then I can carry out regression. So, how to catch all > “test” values from > different dataframes? Or does anyone > have better way to get this target? Once you have all your "test" values, you probably want to perform a regression on all the data, in a single data frame, with "formulation" and "subject" as effects, e.g. lm(test~concentration+formulation+subject, data=df) If the subjects are drawn from a large population, it is better to represent them as random effects in a mixed effects model. library(nlme) lme(test~concentration+formulaion, data=df, random=~1|subject) Regards, Richie. Mathematical Sciences Unit HSL ------------------------------------------------------------------------ ATTENTION: This message contains privileged and confidential information intended for the addressee(s) only. If this message was sent to you in error, you must not disseminate, copy or take any action in reliance on it and we request that you notify the sender immediately by return email. Opinions expressed in this message and any attachments are not necessarily those held by the Health and Safety Laboratory or any person connected with the organisation, save those by whom the opinions were expressed. Please note that any messages sent or received by the Health and Safety Laboratory email system may be monitored and stored in an information retrieval system. ------------------------------------------------------------------------ ------------------------------------------------------------------------ This e-mail message has been scanned for Viruses and Content and cleared by NetIQ MailMarshal ------------------------------------------------------------------------ ______________________________________________ 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.