Change the values of rows conditionally in R

Question

My data looks like this:

company_name <- c("A","A","A","A","B","B","B")
year <- c(1985, 1986, 1987, 1988, 1985, 1986, 1987)
value <- c(0, 1, 0, 0, 1, 0, 0)

df <- data.frame(company_name, year, value)

If the value is 1, I want to switch this row of value (value=1) with the next row (value=0). (group_by should be used for company_name) My output must be like this:

value <- c(0, 0, 1, 0, 0, 1, 0)

new_df <- data.frame(company_name, year, value)

Answer 1

Here is one potential solution:

library(dplyr)

company_name <- c("A","A","A","A","B","B","B")
year <- c(1985, 1986, 1987, 1988, 1985, 1986, 1987)
value <- c(0, 1, 0, 0, 1, 0, 0)

df <- data.frame(company_name, year, value)

answer <- df %>%
  group_by(company_name) %>%
  mutate(value = ifelse(lag(value, default = 0) == 1, lag(value), 0))

value <- c(0, 0, 1, 0, 0, 1, 0)
new_df <- data.frame(company_name, year, value)

all_equal(answer, new_df)
#> [1] TRUE

^{Created on 2022-11-25 by the reprex package (v2.0.1)}