Question

I’m measuring a physiological variable with a millisecond timestamp on a number of patients. For each patient I want to apply a factor to a subset of the timestamped rows describing their posture at that exact moment.

I’ve tried creating the following function, which works fine when describing the first posture. When trying to apply the next “posture-factor,” the previously registered posture is deleted.

TestPatient <- data.frame(Time=seq(c(ISOdatetime(2011,12,22,12,00,00)), by = "sec", length.out = 100),Value=rnorm(100, 9, 3))

patientpositionslice <- function(patient,positiontype,timestart,timestop) {
  patient$Position[
    format(patient$Time, "%Y-%m-%d %H:%M:%S") >= timestart &
    format(patient$Time, "%Y-%m-%d %H:%M:%S") <  timestop] <- positiontype
  patient
}

TestPatientNew <- patientpositionslice(TestPatient,"Horizontal","2011-12-22 12:00:05","2011-12-22 12:00:10")
TestPatientNew <- patientpositionslice(TestPatient,"Vertical","2011-12-22 12:00:15","2011-12-22 12:00:20")

How do I modify the function so I can apply it repeatedly on the same patient with different postures such as “Horizontal”, “Vertical”, “Sitting” etc.?

Answer 1

Here’s your solution. Probably there are more elegant ways but this is mine 😉

 TestPatient <- data.frame(Time=seq(c(ISOdatetime(2011,12,22,12,00,00)), by = "sec",   length.out = 100),Value=rnorm(100, 9, 3))
 #Included column with position
 TestPatient$position <- NA

 patientpositionslice <- function(patient,positiontype,timestart,timestop) {
   #changed the test to ifelse() function
   new<-ifelse(
      format(patient$Time, "%Y-%m-%d %H:%M:%S") >= timestart &
      format(patient$Time, "%Y-%m-%d %H:%M:%S") <  timestop , positiontype, patient$position)
 patient$position <- new
 patient
 }

 TestPatientNew <- patientpositionslice(TestPatient,"Horizontal","2011-12-22 12:00:05","2011-12-22 12:00:10")
 #For repeated insertion use the previous object
 TestPatientNew <- patientpositionslice(TestPatientNew ,"Vertical","2011-12-22 12:00:15","2011-12-22 12:00:20")

i commented the changes. hope it is like you wanted it else just correct me.