Change date of POSIXct variable based on other columns in R - posixct

Question

Is there a way to change the date of a dttm column based on the values from other columns? The time in the "Date_Time" column is correct, but the dates need to be changed to match those in the column "Date" (or from all three columns "Year", "Month", and "Day").
This is likely close to what I need to do, but it gives me this error:
library(lubridate)
df$new <- with(df, ymd_hm(sprintf('%04d%02d%02d', Year, Month, day, Time))) #'Time' is new character column of just time component from 'Date_Time'
# Not sure what this means..
invalid format '%04d'; use format %s for character objects
> head(df,5)
# A tibble: 5 x 5
Date Year Month Day Date_Time
<chr> <fct> <dbl> <dbl> <dttm>
1 2020-11-14 2020 11 14 1899-12-31 10:46:00
2 2020-11-14 2020 11 14 1899-12-31 10:57:00
3 2020-11-14 2020 11 14 1899-12-31 09:16:00
4 2012-8-11 2012 8 11 1899-12-31 14:59:00
5 2012-8-11 2012 8 11 1899-12-31 13:59:00

Answer 1

First update the Date column to be a date. Then use lubridate to assign that date to the Date_Time column:
df$Date <- as.Date(df$Date)
lubridate::date(df$Date_Time) <- df$Date
And if necessary, update the timezone to whatever if needs to be:
attr(df$Date_Time, "tzone") <- "Europe/Paris" # Update timezone