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How to catch data from the different dataframes and lm problem?

3 messages · Richard Cotton, Hsin-Ya Lee

Original
Richard Cotton
# 
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?)
regression,
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


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2 days later
Hsin-Ya Lee
# 
Dear Richie:

1) I have a mistake in the code that ?A.split[[1]][["time"]][i]? should
replace with ?A.split[[j]][["time"]][i]?.  The ?test? value is ?auc? which
is a cumulative rate of change of concentration with respect to time.  

for (j in 1:length(A.split)){
test <- 0
for(i in 2:length(A.split[[j]][["time"]])){
    test[i] <- (A.split[[j]][["time"]][i] - A.split[[j]][["time"]][i-1]) *
(A.split[[j]][["concentration"]][i] - A.split[[j]][["concentration"]][i-1])*
0.5
    test[i]<-test[i]+test[i-1]
 }
output<-data.frame(A.split[[j]][["subject"]],A.split[[j]][["formulation"]],A.split[[j]][["time"]],A.split[[j]][["concentration"]],test)
colnames(output)<-list("subject","formulation","time","concentration","test")
show(output) 
}

subject formulation time   concentration(X) test(Y)
1       1           1    1           0.1  0.00
2       1           1    2          10.0  4.95
3       1           1    3          20.0  9.95
  subject formulation time concentration(X) test(Y)
1       1           2    1            20  0.0
2       1           2    2            25  2.5
3       1           2    3            60  20.0
  subject formulation time concentration(X) test(Y)
1       2           1    1           0.3  0.00
2       2           1    2           2.5  1.10
3       2           1    3           6.0  2.85
  subject formulation time concentration(X) test(Y)
1       2           2    1            35  0.0
2       2           2    2            40  2.5
3       2           2    3            45  5.0

2) Then, I want to pool all "concentration" (X) and pool all "test" (Y) to
perform a 
regression.  For example, I used the ?regression? function of Microsoft
Excel 2003 and intercept is -0.01894 and X is 0.185758.  I think that if I
can catch ?test? (Y) values and ?concentration? (X) values into a dataframe,
then I can use ?lm? to fit linear models.  So, how to catch all ?test?
values from different dataframes?  Or what should I do? 

Best regards,

Hsin-Ya Lee
Hsin-Ya Lee
# 
Dear all:

I used lm to perform a regression in R and and intercept is -0.01894 and X
is 0.185758.  This is my target.  
Y<-(c(0,4.95,9.95,0,2.5,20,0,1.1,2.85,0,2.5,5))
X<-(c(0.1,10,20,20,25,60,0.6,2.5,6,35,40,45))
lm(Y~X)
anova(wnlm<-lm( Y~X))
summary(wnlm<-lm( Y~X))

I catch test (Y) values and concentration (X) values by myself.  Then, here
is my question.  How to ?auto-catch? test (Y) values and concentration (X)
values from the split dataframes?  Because I think that if I can catch
?test? (Y) values and ?concentration? (X) values into a dataframe, then I
can use ?lm? to fit linear models.  So, how to catch all ?test? values from
different dataframes?  Or what should I do? 

Best regards,

Hsin-Ya Lee