Overwriting only NAs in column A with values from column B [duplicate]

Question

I have column Aand column B in a dataframe:

A = structure(c(NA, NA, NA, 1559401558, 1559413729, 1559417798), class = c("POSIXct", 
"POSIXt"), tzone = "")

B = structure(c(1559379600, 1559388600, 1559397600, 1559406600, 1559415600, 
1559424600), class = c("POSIXct", "POSIXt"), tzone = "UTC")
> 

As you can see, only column A has missing Dates. I want now, that only the missing Dates in Aare replaced with related values (same indices) in B. I know this should work with indices, but I can't find a solution for this. Thanks for the help!

Answer 1

Using Base R:

A[is.na(A)] <- B[is.na(A)]

Answer 2

We can use coalesce

library(dplyr) 
coalesce(A, B)

As @RuiBarradas mentioned in the comments, we can set the tz to NULL before doing the coalesce

library(lubridate)
coalesce(A, `tz<-`(B, ""))