Hello
I have a list of POSIXct objects, from which I want to extract those
values that match a specific date, keeping them in POSIXct format. For a
specific date there is 0-2 matching values.
As an example (the actual list and objects are much longer):
x<-list()
x[["first"]]<-as.POSIXct(c("2011-08-27 10:45:00 GMT", "2011-10-30
15:45:00 GMT", "2011-10-30 16:00:00 GMT", "2012-06-22 09:30:00 GMT"))
x[["second"]]<-as.POSIXct(c("2011-08-27 11:00:00 GMT", "2011-10-30
15:30:00 GMT", "2011-10-30 15:45:00 GMT", "2012-06-22 10:00:00 GMT"))
If I use the following expression for one specific object of the list, I
get the result I expect:
x[[1]][as.Date(x[[1]])=="2011/10/30"][1]
[1] "2011-10-30 15:45:00 GMT"
Now if I write a for loop based on that expression to store the values
of interest in a data frame, the POSIXct values are coerced into numeric:
y<-data.frame()
for (i in 1:length(x)) {
y[i,"ID"]<-names(x[i])
y[i,"first"]<-x[[i]][as.Date(x[[i]])=="2011/10/30"][1]
y[i,"second"]<-x[[i]][as.Date(x[[i]])=="2011/10/30"][2]
}
ID first second
1 a 1319989500 1319990400
2 b 1319988600 1319989500
I am a bit confused about why that is.
I could coerce them back to POSIXct with another line of code, but is
there a better way? And is there a way to avoid using a for loop to
complete this task?
No need to say I am quite new to R, so apologies for any obvious mistake
or oversight.
Many thanks
A. Duranel, UCL Department of Geography
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