如何使用自定義函數將因子應用於較大時間序列的不同子集？

Question

我正在測量許多患者的毫秒時間戳的生理變量。對於每個患者，我想在時間戳行的一個子集上應用一個因子，描述他們在那個時刻的姿勢。

我試過創建下面的函數，它在描述第一個姿勢時工作正常。當嘗試應用下一個「姿勢因素」時，先前登記的姿勢被刪除。

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") 

如何修改的功能，這樣我就可以重複它適用於不同的姿勢，如「橫」，「豎」，「坐」等同一患者？

Answer 1

這是您的解決方案。可能有更優雅的方式，但這是我的;）

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") 

我評論了這些變化。希望它像你想要的那樣只是糾正我。