Converting numerics to date format

R 4.6.2
OS X

Colleagues,

I am having a problem with conversion of a numeric to date format.  In the =
example shown below, the first column is the original date value.

The second column is the conversion to numeric.

In the third column, I add 0.5 to the second column.

The fourth column converts the third column back to a date format using the=
 following code:
FORMAT                          <- "%d-%b-%Y %H:%M"
SECPERDAY                       <- 24 * 60 * 60
SUBSUB <- structure(list(PKDOSDTC_PM_RAW =3D c("06-Apr-2025 10:30", "10-Dec=
-2025 07:15",  "11-May-2025 07:30", "16-Mar-2025 08:00", "11-May-2025 08:00=
",  "16-Mar-2025 08:00", "22-Sep-2024 09:00", "11-Aug-2025 09:00",  "20-Oct=
-2024 08:00", "14-Jan-2026 10:00", "03-Nov-2025 08:00"
), PM.ELAPSED =3D c(20184.438, 20432.302, 20219.312, 20163.333,  20219.333,=
 20163.333, 19988.375, 20311.375, 20016.333, 20467.417,  20395.333), FIX.PM=
.ELAPSED =3D c(20184.938, 20432.802, 20219.812,  20163.833, 20219.833, 2016=
3.833, 19988.875, 20311.875, 20016.833,  20467.917, 20395.833), FIX.PM.RAW =
=3D c("06-Apr-2025 15:30", "10-Dec-2025 11:15",  "11-May-2025 12:30", "16-M=
ar-2025 13:00", "11-May-2025 13:00",  "16-Mar-2025 13:00", "22-Sep-2024 14:=
00", "11-Aug-2025 14:00",  "20-Oct-2024 13:00", "14-Jan-2026 14:00", "03-No=
v-2025 12:00"
)), row.names =3D c(36L, 71L, 120L, 183L, 253L, 288L, 316L, 400L,  414L, 50=
5L, 519L), class =3D "data.frame")
SUBSUB$REVISED                  <- format.Date(SUBSUB$nREVISED * SECPERDAY,=
 format=3DFORMAT)

Note the following:
	1.  nREVISED is 0.5 larger than nORIGINAL, i.e., 12 hours
	2.  the difference between REVISED and ORIGINAL is either 4 or 5 hours -- =
I intended it to be 12 hours.

The discrepancy of 8 or 7 hours (12 - [4 or 5]) suggests to me that the pro=
blem involves time times; the occurrence of 4 vs. 5 is presumably due to da=
ylight savings time (PST vs. PDT).

I suspect that the problem can be solved by adding TZ to the code and possi=
bly origin.  But various attempts to do this all fail.

Any suggestions?

Dennis

Dennis Fisher MD
P < (The "P Less Than" Company)
Phone: 415 307-4791
www.PLessThan.com

             ORIGINAL nORIGINAL nREVISED           REVISED
36  06-Apr-2025 10:30  20184.44 20184.94 06-Apr-2025 15:30
71  10-Dec-2025 07:15  20432.30 20432.80 10-Dec-2025 11:15
120 11-May-2025 07:30  20219.31 20219.81 11-May-2025 12:30
183 16-Mar-2025 08:00  20163.33 20163.83 16-Mar-2025 13:00
253 11-May-2025 08:00  20219.33 20219.83 11-May-2025 13:00
288 16-Mar-2025 08:00  20163.33 20163.83 16-Mar-2025 13:00
316 22-Sep-2024 09:00  19988.38 19988.88 22-Sep-2024 14:00
400 11-Aug-2025 09:00  20311.38 20311.88 11-Aug-2025 14:00
414 20-Oct-2024 08:00  20016.33 20016.83 20-Oct-2024 13:00
505 14-Jan-2026 10:00  20467.42 20467.92 14-Jan-2026 14:00
519 03-Nov-2025 08:00  20395.33 20395.83 03-Nov-2025 12:00