按多列分组并从R中的另一列分配值

df %>%
  group_by(Temp) %>%
  mutate(`Starting Output` = ifelse(Time==0, Output, NA)) %>%
  tidyr::fill(`Starting Output`, .direction = "down") %>%
  ungroup()

# A tibble: 6 x 5
  Batch  Temp  Time Output `Starting Output`
  <chr> <dbl> <dbl>  <dbl>             <dbl>
1 A        15     0     12                12
2 A        15    24     34                12
3 A        15    48     36                12
4 A        25     0     13                13
5 A        25    24     22                13
6 A        25    48     24                13