R: data.table using a for loop to wrangle multiple columns - r

Question

I am currently working in R to build a for loop which will add the year to 7 columns that contain partial dates (dd/mm). I have been attempting to run the following for-loop and have not been successful. What am I doing wrong?
Here's a sample of what my data set looks like (The actual data set includes columns HomDate - HomDate_7 but I only included the first few as I know you'll get the point...)
Participant DateVisit HomDate HomDate_2 HomeDate_3 year_flag
1 2012-04-25 18/04 19/04 20/04 NA
2 2012-01-04 28/12 29/12 30/12 1
3 2012-01-05 31/12 01/01 01/02 1
4 2012-06-13 06/06 07/06 08/06 NA
5 2012-02-12 05/02 06/02 07/02 NA
Here's the code I've been trying to use:
hom_date <- list("HomDate", "HomDate_2", "HomDate_3", "HomDate_4", "HomDate_5", "HomDate_6",
"HomDate_7")
set_dates <- function(x){
home_morbid[,x:=as.character(x)]
home_morbid[(substr(x, 4, 5)==12) & (year_flag==1), x:=paste(x, "/2011", sep="")]
home_morbid[(substr(x, 4, 5)==01) & (year_flag==1), x:=paste(x, "/2012", sep="")]
home_morbid[is.na(year_flag), x:=paste(x, "/", substr(DateVisit, 1, 4), sep="")]
}
for(i in 1:length(hom_date)){
x <- hom_date[i]
home_morbid_2<-set_dates(x)
}

Answer 1

I'm not sure what happens to those with an NA flag. Here is an approach:
to_replace<-grep("^Hom",names(df))
df[,(to_replace):=lapply(.SD, function(x) ifelse(is.na(year_flag),x,
ifelse(substr(x, 4, 5)==12,
paste0(x,"/","2011"),
paste0(x,"/","2012")))),
.SDcols=HomDate:HomeDate_3][]
Participant DateVisit HomDate HomDate_2 HomeDate_3 year_flag
1: 1 2012-04-25 18/04 19/04 20/04 NA
2: 2 2012-01-04 28/12/2011 29/12/2011 30/12/2011 1
3: 3 2012-01-05 31/12/2011 01/01/2012 01/02/2012 1
4: 4 2012-06-13 06/06 07/06 08/06 NA
5: 5 2012-02-12 05/02 06/02 07/02 NA
To replace NA flagged years with the year from DateVisit:
library(lubridate)
to_replace<-grep("^Hom",names(df))
df[,(to_replace):=lapply(.SD, function(x) ifelse(is.na(year_flag),
paste0(x,"/",year(ymd(DateVisit))),
ifelse(substr(x, 4, 5)==12,
paste0(x,"/","2011"),
paste0(x,"/","2012")))),
.SDcols=HomDate:HomeDate_3][]
Participant DateVisit HomDate HomDate_2 HomeDate_3 year_flag
1: 1 2012-04-25 18/04/2012 19/04/2012 20/04/2012 NA
2: 2 2012-01-04 28/12/2011 29/12/2011 30/12/2011 1
3: 3 2012-01-05 31/12/2011 01/01/2012 01/02/2012 1
4: 4 2012-06-13 06/06/2012 07/06/2012 08/06/2012 NA
5: 5 2012-02-12 05/02/2012 06/02/2012 07/02/2012 NA