Add rows with specific values in between existing rows

Question

I have hockey data, called df

structure(list(event_index = 1:57, coords_x = c(80, 53, 31, -56, 
-34, -33, -40, 30, -66, -36, 45, 17, -6, 47, -51, -31, -69, -86, 
-70, 80, 65, -76, -71, 81, -57, 80, 75, 77, -71, -40, -83, 62, 
77, 76, NA, -61, 69, -45, 68, 31, 58, 61, 80, 34, 80, -85, -37, 
-57, 76, 14, 49, -82, -34, -36, -83, -84, -55), coords_y = c(-1, 
14, -30, 17, 26, -23, -37, 17, -32, -18, 25, 17, -38, 21, 28, 
22, 17, 13, 10, -37, -17, 9, 18, -11, 21, -7, 3, 3, -38, 31, 
8, -30, -2, 4, NA, -5, 15, 10, -30, -34, 20, 27, -4, 8, -18, 
19, 32, -21, 0, 40, -4, -30, -24, -28, -2, -3, 34), event_rinkside = c("R", 
"R", "R", "L", "L", "L", "L", "R", "L", "L", "R", "N", "N", "R", 
"L", "L", "L", "L", "L", "R", "R", "L", "L", "R", "L", "R", "R", 
"R", "L", "L", "L", "R", "R", "R", NA, "L", "R", "L", "R", "R", 
"R", "R", "R", "R", "R", "L", "L", "L", "R", "N", "R", "L", "L", 
"L", "L", "L", "L")), class = c("tbl_df", "tbl", "data.frame"
), row.names = c(NA, -57L))

How do I create rows after every single row, leaving me with 57 * 2 (114 rows), but the values in my newly created rows depend on event_rinkside column.

• If event_rinkside equals R, then, I want to insert 82 into coords_x and 0 into coords_y.
• If event_rinkside equals L, then, I want to insert -82 into coords_x and 0 into coords_y.

I feel like the solution to this SO question is a good starting points, but I don't know how to incorporate my own conditions:

Here is the solution I'm talking about:

library(purrr)
df %>%
  group_by(id) %>%
  map_dfr(rbind, NA) %>%
  mutate(id = rep(df$id, each = 2))

Answer 1

Here's a solution with dplyr:

library(dplyr)

df %>%
  mutate(coords_x = 82 * ifelse(event_rinkside == "L", -1, 1),
         coords_y = 0) %>%
  rbind(df, .) %>%
  arrange(event_index)

How it works:

In the first step, mutate is used to modify an unassigned copy of df. The column coords_x gets the value of 82; the value is multiplied with -1 if event_rinkside == "L" and 1 otherwise. The column coords_y gets the value of 0.

In the next step, the unchanged original data frame df and the current unassigned and modified copy of it are combined with rbind. Here, . represents the result of the mutate step above. The result of rbind has the rows of the original version above the rows of the modified version.

In the last step, arrange is used to sort the rows along the values of event_index. In this way, each original row is directly followed by the corresponding modified row.

The result:

# A tibble: 114 x 4
   event_index coords_x coords_y event_rinkside
         <int>    <dbl>    <dbl> <chr>         
 1           1       80       -1 R             
 2           1       82        0 R             
 3           2       53       14 R             
 4           2       82        0 R             
 5           3       31      -30 R             
 6           3       82        0 R             
 7           4      -56       17 L             
 8           4      -82        0 L             
 9           5      -34       26 L             
10           5      -82        0 L             
# … with 104 more rows