Convert from military time to UTC in R - r

Question

I have a dataset, df1, I would like to convert all the values from the 24 hour clock to UTC.
Date Name
1/2/2020 16:46 A
1/2/2020 16:51 B
I Would like
Date Name
1/2/2020 4:46:47 PM A
1/2/2020 4:51:44 PM B
I have tried:
df$Date<- format(df$Date, "%m/%d/%Y %I:%M:%S %p")
dput:
structure(list(Date = structure(1:2, .Label = c("1/2/2020 16:46",
"1/2/2020 16:51"), class = "factor"), Name = structure(1:2, .Label = c("A",
"B"), class = "factor")), class = "data.frame", row.names = c(NA,
-2L))

Answer 1

You can first convert the data to POSIXct format and then use format to get data in the required format.
df$Date <- format(as.POSIXct(df$Date, format = "%m/%d/%Y %H:%M"),
"%m/%d/%Y %I:%M:%S %p")
#Can also use mdy_hm from lubridate
#df$Date <- format(lubridate::mdy_hm(df$Date), "%m/%d/%Y %I:%M:%S %p")
df
# Date Name
#1 01/02/2020 04:46:00 PM A
#2 01/02/2020 04:51:00 PM B

Answer 2

Assuming you want to actually convert a string in one format to a string in another format rather than having it as a (more useful) actual date/time, you can use a little arithmetic and string chopping along with mapply:
splits <- strsplit(as.character(df$Date), " |:")
Hours <- as.numeric(sapply(splits, `[`, 2))
AMPM <- c(" AM", " PM")[Hours %/% 12 + 1]
Hours <- Hours %% 13 + Hours %/% 13
df$Date <- mapply(function(x, y, z) paste0(x[1], " ", y, ":", x[3], z), splits, Hours, AMPM)
df
#> Date Name
#> 1 1/2/2020 4:46 PM A
#> 2 1/2/2020 4:51 PM B
Created on 2020-02-26 by the reprex package (v0.3.0)

Answer 3

Assuming the same assumptions as the previous answer by Allan, here is another way of converting from 24 hour to 12 hour.
library(tidyverse)
library(lubridate)
df <- tibble(
date = c(ymd_hms("2020/01/02 16:46:00", "2020/01/02 16:51:00", tz = "UTC")),
name = c("A", "B")
)
df %>%
mutate(date_hour = hour(date),
am_pm = if_else(date_hour > 12, "PM", "AM"),
date_hour = if_else(date_hour > 12, date_hour - 12, date_hour - 0),
newdatetime = paste0(date(date), " ", date_hour , ":", minute(date), " ", am_pm)) %>%
select(-c(date_hour, am_pm))
df
# A tibble: 2 x 3
date name newdatetime
<dttm> <chr> <chr>
1 2020-01-02 16:46:00 A 2020-01-02 4:46 PM
2 2020-01-02 16:51:00 B 2020-01-02 4:51 PM
Hope this helps!