通过在数据框中使用标志添加垂直线

Question

I have a data frame as follows:

df<-
 FORM  TIME   CONC  
  0     1      5
  0     2      10 
  0     5      11
  1     6      14
  1     7      15

I am plotting TIME versus CONC . I would like to add a vertical line at the TIME when the formulation changes from FORM 1 to FORM 2 . I want to make my code for plotting so it can detect when the formulation changes automatically.

How should I write it in the ggplot line below:

plotobj <- plotobj + vline(aes(slope = 1, intercept = ??), linetype = "dashed", size = 1)

Answer 1

If I read you correctly, this should help out:

library(ggplot2)

df = data.frame(FORM=c(0,0,0,1,1),TIME=c(1,2,5,6,7),CONC=c(5,10,11,14,15))

ggplot()+
   geom_line(data=df,aes(x=TIME,y=CONC))+
   geom_vline(xintercept = min(df$TIME[grep(1,df$FORM)]), linetype = "dashed", size = 1)

What is actually important:

min(df$TIME[grep(1,df$FORM)])

grep gives indexes for all FORM values equal to 1. We extract these and chose the one from the row with the smallest value of TIME using min . Finally using this index we pick the correponding value from df$TIME .