Coalescing multiple columns from both the left and right side - r

Question

Given the following data
df1 <- structure(list(ID = 1:3, alpha_1 = c(2L, 2L, 3L),
alpha_2 = c(1L, 2L,
3L), alpha_3 = c(4L, 4L, 2L), alpha_4 = c(3L, NA, NA), beta_1 = c(NA,
2L, NA), beta_2 = c(3L, NA, 2L), charlie_1 = c(1L, NA, 1L), charlie_2 = c(NA,
2L, NA)), class = "data.frame", row.names = c(NA, -3L))
I'm trying to coalesce all columns sharing the same initial prefix name (i.e. coalesce alpha_1, alpha_2, alpha_3, alpha_4, and coalesce beta_1 beta_2, etc.), but from both the left and right sides. That is, I want to generate two new variables, say 'alpha_left' and 'alpha_right', whose columns would be, in this example, (2, 2, 3) and (3, 4, 2) respectively (first non-missing elements from the left and right side of the dataframe).
User #akrun offered a great solution for the coalescing part here, but I'm unsure how to create two new variables from both the left and right coalesces.

Answer 1

Here is an option in tidyverse
Reshape to 'long' format - pivot_longer
Grouped by 'ID'
Do the summarise across the columns 'alpha' till 'charlie'
Get the column name - cur_column()
Create a tibble with the first non-NA element from the left and the right
Change the column names by appending the 'nm1' as prefix
Finally, unnest the list columns created in summarise
library(dplyr)
library(tidyr)
library(stringr)
df1 %>%
pivot_longer(cols = contains("_"),
names_to = c( ".value", "grp"), names_sep = "_") %>%
group_by(ID) %>%
summarise(across(alpha:charlie, ~ {
nm1 <- cur_column()
tbl1 <- tibble(left= .[complete.cases(.)][1],
right = rev(.)[complete.cases(rev(.))][1]);
names(tbl1) <- str_c(nm1, "_", names(tbl1))
list(tbl1)})) %>%
unnest(c(alpha, beta, charlie))
-output
# A tibble: 3 x 7
ID alpha_left alpha_right beta_left beta_right charlie_left charlie_right
<int> <int> <int> <int> <int> <int> <int>
1 1 2 3 3 3 1 1
2 2 2 4 2 2 2 2
3 3 3 2 2 2 1 1
Or using base R
lst1 <- lapply(split.default(df1[-1], sub("_\\d+$", "", names(df1)[-1])),
function(x) {
x1 <- apply(x, 1, function(y) {
y1 <- na.omit(y)
if(length(y1) > 1 ) y1[c(1, length(y1))] else y1[1]
})
if(is.vector(x1)) as.data.frame(matrix(x1)) else as.data.frame(t(x1))
})

Answer 2

You could also do:
df1[-1] %>%
split.default(sub("_\\d+", "", names(.))) %>%
imap_dfc(~data.frame(right = coalesce(!!!.x),
left = coalesce(!!!rev(.x))) %>%
set_names(paste(.y, names(.), sep="_")))
alpha_right alpha_left beta_right beta_left charlie_right charlie_left
1 2 3 3 3 1 1
2 2 4 2 2 2 2
3 3 2 2 2 1 1

Answer 3

One more approach not as elegant as #Onyambu's
library(tidyverse)
df1[-1] %>%
split.default(sub("_\\d+", "", names(.))) %>%
imap_dfc(~ .x %>% rowwise() %>%
mutate(!!paste0(.y, '_left') := head(na.omit(c_across(everything())),1),
!!paste0(.y, '_right') := tail(na.omit(c_across(!last_col())),1),
.keep = 'none' )
)
#> # A tibble: 3 x 6
#> # Rowwise:
#> alpha_left alpha_right beta_left beta_right charlie_left charlie_right
#> <int> <int> <int> <int> <int> <int>
#> 1 2 3 3 3 1 1
#> 2 2 4 2 2 2 2
#> 3 3 2 2 2 1 1
Created on 2021-06-19 by the reprex package (v2.0.0)

Answer 4

Another option
library(tidyverse)
df1 <- structure(list(ID = 1:3, alpha_1 = c(2L, 2L, 3L),
alpha_2 = c(1L, 2L,
3L), alpha_3 = c(4L, 4L, 2L), alpha_4 = c(3L, NA, NA), beta_1 = c(NA,
2L, NA), beta_2 = c(3L, NA, 2L), charlie_1 = c(1L, NA, 1L), charlie_2 = c(NA,
2L, NA)), class = "data.frame", row.names = c(NA, -3L))
df1 %>%
pivot_longer(cols = -ID, names_sep = "_", names_to = c(".value", "set")) %>%
group_by(ID) %>%
fill(alpha:charlie, .direction = "updown") %>%
filter(set %in% range(set)) %>%
mutate(set = c("left", "right")) %>%
pivot_wider(id_cols = ID, names_from = set, values_from = alpha:charlie)
#> # A tibble: 3 x 7
#> # Groups: ID [3]
#> ID alpha_left alpha_right beta_left beta_right charlie_left charlie_right
#> <int> <int> <int> <int> <int> <int> <int>
#> 1 1 2 3 3 3 1 1
#> 2 2 2 4 2 2 2 2
#> 3 3 3 2 2 2 1 1
Created on 2021-06-20 by the reprex package (v2.0.0)