Lagged differences between specific comparison with distinct number of cases

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I am in need of a column with "lagged differences" between specific comparison. In the data structure I have some case repetitions and I can't just assign lag =1. I also need the output with all cases filled and with the distinct direction (sign) of the comparison.

Take a look at the structure:

df <- structure(
  list(
    id = c(1, 1, 2, 2, 3, 3, 3, 4, 4, 4),
    H_A = c("H",
            "A", "H", "A", "H", "H", "A", "H", "A", "A"),
    Rk = c(6, 15, 19,
           7, 8, 8, 10, 12, 3, 3)
  ),
  row.names = c(NA,-10L),
  class = c("tbl_df",
            "tbl", "data.frame")
)

I need this output:

enter image description here

The closest output I could get was using:

df %>% 
  group_by(id) %>% 
  mutate(Rk_diff = Rk-Rk[match('A', H_A)]) %>%
  ungroup
difference tidyverse r
1 Answers

We could replace the 0's in the next step

library(dplyr)
df %>%
   group_by(id) %>%
    mutate(Rk_diff = Rk - Rk[match('A', H_A)],
    Rk_diff = replace(Rk_diff, Rk_diff == 0, -1 * (Rk_diff[H_A != 'A'][1]))) %>% 
   ungroup

-output

# A tibble: 10 × 4
      id H_A      Rk Rk_diff
   <dbl> <chr> <dbl>   <dbl>
 1     1 H         6      -9
 2     1 A        15       9
 3     2 H        19      12
 4     2 A         7     -12
 5     3 H         8      -2
 6     3 H         8      -2
 7     3 A        10       2
 8     4 H        12       9
 9     4 A         3      -9
10     4 A         3      -9

Or another option is coalesce

library(tidyr)
df %>%
   group_by(id) %>%
   mutate(Rk_diff = case_when(H_A != 'A' ~ Rk - Rk[match('A', H_A)]), 
    Rk_diff2 = -1 * Rk_diff) %>%
    fill(Rk_diff2) %>% 
    ungroup %>% 
    mutate(Rk_diff = coalesce(Rk_diff, Rk_diff2), Rk_diff2 = NULL)

-output

# A tibble: 10 × 4
      id H_A      Rk Rk_diff
   <dbl> <chr> <dbl>   <dbl>
 1     1 H         6      -9
 2     1 A        15       9
 3     2 H        19      12
 4     2 A         7     -12
 5     3 H         8      -2
 6     3 H         8      -2
 7     3 A        10       2
 8     4 H        12       9
 9     4 A         3      -9
10     4 A         3      -9
user_37322710
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