On 08/12/2023 4:30 p.m., David Winsemius wrote:
On 12/7/23 08:21, Sorkin, John wrote:
Colleagues,
I have a matrix of character data that represents date and time. The format of
each element of the matrix is
"2020-09-17_00:00:00"
How can I convert the elements into a valid R date-time constant?
You will not be able to store these datetime values in an R matrix, at
least as class POSIXct. You could with class POSIXlt, but I've not seen
it used before but it does appear possible since matrices can contain
lists.
R matrices do no provide the capability to assign attributes, so only
atomic types and lists can be elements. If you wanted to maintain the
same structure, your first step might be to coerce to a data.frame and
then proceed, or to first construct a vector and then use as the first
argument to `matrix`.
The general sentiment is correct (it's hard to put POSIXct elements in
matrices), but it's not impossible. Almost all R objects can have
attributes.
For example,
m <- matrix(Sys.time(), 2,2)
converts the time to a numerical value, but you can view it as a POSIXlt
object using
class(m) <- c("POSIXct", class(m))
Subsetting works, e.g. m[1,1] is a time, etc.
Duncan Murdoch
Best;
David
Thank you,
John
John David Sorkin M.D., Ph.D.
Professor of Medicine, University of Maryland School of Medicine;
Associate Director for Biostatistics and Informatics, Baltimore VA Medical
Center Geriatrics Research, Education, and Clinical Center;
PI Biostatistics and Informatics Core, University of Maryland School of
Medicine Claude D. Pepper Older Americans Independence Center;
Senior Statistician University of Maryland Center for Vascular Research;
Division of Gerontology and Paliative Care,
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
Cell phone 443-418-5382
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