[R] miscalculate AUC

[leeznar at yahoo.com.tw]

Dear R-helper,

I have subject 1, 2, 3 and formulation S, MF, MM.  I
have a problem in calculating AUC.  The AUC (0~t) in
formulation MF and MM were miscalculated, but I don’t
know where my problem is.  Here is my code and output.

test<-function( InVVTestindex, 
              separateWindows=TRUE)
 {                  
   for( i in 1:length(unique
(InVVTestindex$subject))){
       x<-InVVTestindex$time[InVVTestindex$subject==i]
      
y<-InVVTestindex$concentration[InVVTestindex$subject==i]
      
v<-InVVTestindex$formulation[InVVTestindex$subject==i]
       w<-InVVTestindex$pH[InVVTestindex$subject==i]
       #calculate AUC  
       add<-function(time,concentration){
       auc<-0
       for(i in 2:length(time)) {
      
auc[i]<-1/2*(time[i]-time[i-1])*(concentration[i]+concentration[i-1])
       auc[i]<-auc[i]+auc[i-1]
       }
       return(list(auc=auc))
       }
       add<-add(x,y)
       AUC<-add$auc
       #Output   
       cat("<< Output >>\n")  
       output<-data.frame(w,i,v,x,y,AUC)
      
colnames(output)<-list("pH","subject","formulation","time","concentration","AUC(0~t)")
       show(output)  
       cat("\n\n")
      }    
 }    


<< Output >>
    pH subject formulation time concentration 
AUC(0~t)
1  6.8       1           S  0.0          0.00   
0.0000
2  6.8       1           S  0.5        110.26  
27.5650
3  6.8       1           S  1.0        116.17  
84.1725
4  6.8       1           S  1.5        130.20 
145.7650
5  6.8       1           S  2.0        145.77 
214.7575
6  6.8       1           S  3.0        123.75 
349.5175
7  6.8       1           S  4.0        123.05 
472.9175
8  6.8       1           S  5.0         82.35 
575.6175
9  6.8       1           S  6.0         48.62 
641.1025
10 6.8       1           S  8.0         26.51 
716.2325
11 6.8       1           S 10.0          3.04 
745.7825
12 6.8       1           S 12.0          2.87 
751.6925
13 6.8       1           S 24.0          2.74 
785.3525
14 6.8       1          MF  0.0         0.00  752.4725
15 6.8       1          MF  0.5         91.67 
775.3900
16 6.8       1          MF  1.0        216.78 
852.5025
17 6.8       1          MF  1.5        179.91 
951.6750
18 6.8       1          MF  2.0        187.02
1043.4075
19 6.8       1          MF  3.0        176.15
1224.9925
20 6.8       1          MF  4.0        171.24
1398.6875
21 6.8       1          MF  5.0        157.83
1563.2225
22 6.8       1          MF  6.0        149.15
1716.7125
23 6.8       1          MF  8.0        142.18
2008.0425
24 6.8       1          MF 10.0        107.56
2257.7825
25 6.8       1          MF 12.0         86.37
2451.7125
26 6.8       1          MF 24.0          9.30
3025.7325
27 6.8       1          MM  0.0          0.00
2914.1325
28 6.8       1          MM  0.5        114.18
2942.6775
29 6.8       1          MM  1.0        160.72
3011.4025
30 6.8       1          MM  1.5        152.28
3089.6525
31 6.8       1          MM  2.0        125.05
3158.9850
32 6.8       1          MM  3.0        118.97
3280.9950
33 6.8       1          MM  4.0        123.26
3402.1100
34 6.8       1          MM  5.0        143.46
3535.4700
35 6.8       1          MM  6.0        137.00
3675.7000
36 6.8       1          MM  8.0         91.48
3904.1800
37 6.8       1          MM 10.0         52.46
4048.1200
38 6.8       1          MM 12.0         15.39
4115.9700
39 6.8       1          MM 24.0          8.00
4256.3100


Best regards,
Hsin-Ya Lee