How to select date range with POSIXct type

Question

I'm working on a project where I want to track birth totals nine months after another event (wondering if there is a correlation). It was suggested I use the "lubridate" package to combine MONTH and YEAR in my data frames (which I was seeking to do).

I have successfully used lubridate in both data frames. The problem is that I only want to select a certain date range from one of those data frames, and I'm having difficulty doing this. I think it's because the type of data is POSIXct:

str(model.weather)
'data.frame':   467 obs. of  2 variables:
 $ DATE      : POSIXct, format: "2006-01-01" "2006-01-01" "2006-01-01" "2006-01-01" ...
 $ EVENT_TYPE: Factor w/ 8 levels "Hail","Heavy Snow",..: 2 2 2 2 2 2 3 2 3 3 ...

I have tried converting to numeric, but unfortunately that does horrible, horrible things to the data in my DATE variable. I've tried converting to factor, character, and integer, too - none of them seem to work.

I'm trying to use the "subset" function to select the necessary date range:

model.weather <- subset(model.weather, DATE >= 2006-04-01 | DATE <= 2011-03-01)

Unfortunately, this just returns the original data, without doing any filtering.

Can anyone help?

Solution

If DATE contains only dates (without hours and etc, like in your example data above) you can convert it into as.Date class and then operate on it

model.weather$DATE <- as.Date(model.weather$DATE)

model.weather <- subset(model.weather, DATE >= "2006-04-01" & DATE <= "2011-03-01")

or (a better solution)

model.weather <- model.weather[model.weather$DATE >= "2006-04-01" & model.weather$DATE <= "2011-03-01", ]

Comments

[thebonafortuna]

Thanks, David. Converting to as.Date helped, and your second (better) solution got me the rest of the way there!