Iain,
Just to throw out another option, using base R functions:
test <- c('08-04-22', '08-07-28', '09-03-02', '09-03-03', '09-01-30',
'09-03-09', '10-02-24', '10-03-05')
> median(as.numeric(diff(as.Date(test, format = "%y-%m-%d"), lag = 4) / 30.44))
[1] 10.54534
This uses the ?diff function which has a Date method (defaulting to units in
days) and also a 'lag' option:
> diff(as.Date(test, format = "%y-%m-%d"), lag = 4)
Time differences in days
[1] 283 224 359 367
I use 30.44 above to convert days to months.
HTH,
Marc Schwartz
On Jun 29, 2011, at 10:50 AM, Iain Gallagher wrote:
> Typical - you post to the list and then work it out for yourself!
>
> Anyway here's my solution
>
> Toy code as before then:
>
> intervalsMonths <- 12 * intervals$year + intervals$month
>
> #convert whole years to months then add the remaining months for that entry
> in intervals
>
> medianMonths <- median(as.numeric(intervalsMonths))
>
> Best
>
> iain
>
> --- On Wed, 29/6/11, Iain Gallagher <iaingallag...@btopenworld.com> wrote:
>
>> From: Iain Gallagher <iaingallag...@btopenworld.com>
>> Subject: [R] median time period
>> To: r-help@r-project.org
>> Date: Wednesday, 29 June, 2011, 16:24
>> Hello List
>>
>> I'm trying to calculate the median period (in months) of a
>> set of time intervals (between two interventions).
>>
>> I have been playing with the lubridate package to create
>> the intervals but I can't think of the right approach to get
>> the median timeperiod.
>>
>> Toy code:
>>
>> library(lubridate)
>> test <- c('08-04-22', '08-07-28', '09-03-02',
>> '09-03-03', '09-01-30', '09-03-09', '10-02-24', '10-03-05')
>> test <- ymd(test)
>> intervals <- as.period(test[5:8] - test[1:4])
>>
>> intervals
>> [1] 9 months and 8 days 7 months and 9
>> days 11 months and 22 days
>> [4] 1 year and 2 days
>>
>> How can I convert this 'period' object to months? From
>> there I think I should just convert to 'numeric' and
>> calculate the median.
>>
>> Garrett if you're out there - great package but could you
>> help please!?
>>
>> Best
>>
>> iain
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