[R] adding a date column with dplyr

[MacQueen, Don]

What's wrong with this?

df$Night <- as.POSIXct( paste(format(df$Date,'%Y-%m-%d'),'21:30'))
  or
df$Night <- trunc(df$Date,'day') + 21*60*60 + 30*60

I believe both of those satisfy "the day of tracking for each animal, but
with the time of 21:30". But perhaps you meant the day that tracking
started, when tracking lasted more than one day...


And then just add 24 hours ("one day later") to that one special case

df$Night[df$ID=='M16c'] <- df$Night[df$ID=='M16c'] + 24*60*60

-Don


-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 8/5/16, 9:51 AM, "R-help on behalf of Alice Domalik"
<r-help-bounces at r-project.org on behalf of 9add2 at queensu.ca> wrote:

>Hi all,
>
>
>I'm having some difficulties adding a conditional element to my code.
>
>I have a time series data set that contains GPS tracking coordinates for
>a population of animals.
>
>
>ID                Date                                   Latitude
>  Longitude
>15K12         2014-05-22 04:33:00     50.67675        -129.6553
>
>15K12         2014-05-22 04:35:00     50.45613        -129.4566
>15K19         2014-05-24 06:44:00     50.34611        -129.5678    (and
>so on)
>
>I added a new column to this dataset, called "Night", which is the day of
>tracking for each animal, but with the time of 21:30.
>
>
>ID                Date                                  Latitude
> Longitude       Night
>15K12         2014-05-22 04:33:00     50.67675        -129.6553
>2014-05-22 21:30:00
>
>15K12         2014-05-22 04:35:00     50.45613        -129.4566
>2014-05-22 21:30:00
>15K19         2014-05-24 06:44:00     50.34611        -129.5678
>2015-05-24 21:30:00
>
>I used the following code to do this:
>library(dplyr)
>library(lubridate)
>Sys.setenv(TZ="Canada/Pacific")
>df<-df%>%
>  group_by(ID) %>%
>  mutate(Night=as.POSIXct(date(min(Date)) + days(0) + hours(21) +
>minutes(30), tz="Canada/Pacific"))
>
>However, I need to add a conditional element, because for one animal,
>"Night" needs to be 1 day later. I tried this code...
>
>df<-df%>%
>  group_by(ID) %>%
>  mutate(Night=ifelse(test=(id=='M16c'),yes=as.POSIXct(date(min(Date)) +
>days(1) + hours(21) + minutes(30), tz="Canada/Pacific"),
>no=as.POSIXct(date(min(Date)) + days(0) + hours(21) + minutes(30),
>tz="Canada/Pacific")))
>
>The code runs, but instead of having a date, I get a string of numbers
>like "1403497200" in the column "Night".
>Any ideas what the problem could be?
>
>Thanks, Alice
>
>
>
>
>	[[alternative HTML version deleted]]
>
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