R fill in NA with previous row value with condition

Question

I need to fill in NA rows with the previous row value, but only until a criteria is not changed. As a simple example for days of week, meals and prices:

Day = c(         


        

Answer 1

Another option using data.table

library(data.table)
library(xts)

dt <- data.table(df)

dt[, Price := na.locf(Price, fromLast = TRUE), by = Meal]