calculating number of days between 2 columns of dates in data frame
You could find the difference between dates in columns in a data frame by using the function difftime
as follows:
df$diff_in_days<- difftime(df$datevar1 ,df$datevar2 , units = c("days"))
Without your seeing your data (you can use the output of dput(head(survey))
to show us) this is a shot in the dark:
survey <- data.frame(date=c("2012/07/26","2012/07/25"),tx_start=c("2012/01/01","2012/01/01"))
survey$date_diff <- as.Date(as.character(survey$date), format="%Y/%m/%d")-
as.Date(as.character(survey$tx_start), format="%Y/%m/%d")
survey
date tx_start date_diff
1 2012/07/26 2012/01/01 207 days
2 2012/07/25 2012/01/01 206 days
You need to use the as.Date formats correctly.
Eg.
x = '2012/07/25'
xd = as.Date(x,'%Y/%m/%d')
xd # Prints "2012-07-25"
R date formats are similary to *nix ones.
Doing a typeof(xd) shows it as a double ie. days since 1970.