replace the values in column depends on another column

[sai_matcha]

my dataset looks like

df <- data.frame( ID= c(1,1,2,2,3,3,4,4), 
                   TIME = c(0,10,0,20,0,25,0,44),
                   DV = C(0.25,0.25,5,5,6,6,7,7))                      

i want to make DV as NA whenever TIME is 0

[technocrat]

suppressPackageStartupMessages({library(dplyr)})
# avoid built-in identifier df
dat <- data.frame( ID= c(1,1,2,2,3,3,4,4), 
                  TIME = c(0,10,0,20,0,25,0,44),
                  DV = c(0.25,0.25,5,5,6,6,7,7)) # not C

dat %>% mutate(DV = ifelse(TIME == 0,NA,TIME))
#>   ID TIME DV
#> 1  1    0 NA
#> 2  1   10 10
#> 3  2    0 NA
#> 4  2   20 20
#> 5  3    0 NA
#> 6  3   25 25
#> 7  4    0 NA
#> 8  4   44 44

^{Created on 2020-09-16 by the reprex package (v0.3.0)}