将日期分为周和年

Question

Currently my dataframe has dates displayed in the 'Date' column as 01/01/2007 etc I would like to convert these into a week/year value ie 01/2007. Any ideas? I have been trying things like this and getting no where...

enviro$Week <- strptime(enviro$Date, format= "%W/%Y")

Answer 1

You have to first convert to date, then you can convert back to the week of the year using format, for example:

### Converts character to date
test.date <- as.Date("10/10/2014", format="%m/%d/%Y")

### Extracts only Week of the year and year
format(test.date, format="Week number %W of %Y")
[1] "Week number 40 of 2014"

### Or if you prefer
format(date, format="%W/%Y")
[1] "40/2014"

So, in your case, you would do something like this:

enviro$Week <- format(as.Date(enviro$Date, format="%m/%d/%Y"), format= "%W/%Y")

But remember that the part as.Date(enviro$Date, format="%m/%d/%Y") is only necessary if your data is not in Date format, and you also should put the right format parameter to convert your character to Date, if that is the case.

Answer 2

What is the class of enviro$Date ? If it is of class Date there is probably a better way of doing this, otherwise you can try

v <- strsplit(as.character(enviro$Date), split = "/")
weeks <- sapply(v, "[", 2)
years <- sapply(v, "[", 3)
enviro$Week <- paste(weeks, years, sep = "/")