I'm new to R and cannot make plotting work as desired. The problem is that R seems to draw the same four lines over and over again, redundantly. The details of the case I'm having are as follows.
I have a dataset:
> str(dataset)
'data.frame': 57641 obs. of 3 variables:
$ duration : num 3 8 7 2 4 8 2 2 8 8 ...
$ graduated: logi FALSE TRUE TRUE FALSE FALSE TRUE ...
$ group : num 651 651 671 671 651 651 651 651 651 651 ...
Then, I fit a Cox proportional hazards regression model to it:
survObj <- Surv(time = dataset$duration / 2, event = dataset$graduated)
model <- coxph(survObj ~ group, data=dataset)
Next, following this example, I create a frame that would hopefully group the survival functions by the group number:
frame <- data.frame(group = dataset$group)
> str(frame)
'data.frame': 57641 obs. of 1 variable:
$ group: num 651 651 671 671 651 651 651 651 651 651 ...
There's four groups in the data:
> unique(dataset$group)
[1] 651 671 652 681
Using this new frame, I create a fitted survival model:
fitObjGrouped <- survfit(model, newdata = frame)
Finally, I plot the thing:
color_set <- rainbow(4)
plot(fitObjGrouped, col=color_set)
The result has the correct lines, but drawn many times over each other:
As you can see, there's two red lines and two blue lines drawn last. They're the correct ones, one for each category, but closer observation reveals that there's a green or other color lines underneath each of them. When converting this to PDF the file size is 273 times larger than what it should be!
So the question is: why is R drawing the lines so many many times and how could I achieve correct model fitting and plotting at the same time?
Can somebody please help me to better understand the R commands I'm using? Thanks in advance!
