replace the last non-na entry in each row from left to right with the value from the new_col column in a dataset of many columns in r

main.r
# Load necessary libraries
library(dplyr)

# Create a sample dataframe
df <- data.frame(
  col1 = c(1, 2, NA, 4),
  col2 = c(NA, 3, 5, NA),
  col3 = c(6, NA, 7, 8),
  new_col = c("a", "b", "c", "d")
)

# Define a custom function to replace the last non-NA entry
replace_last_non_na <- function(row, new_value) {
  # Find the last non-NA entry
  last_non_na_pos <- max(which(!is.na(row)))
  
  # Replace the last non-NA entry with the new value
  row[last_non_na_pos] <- new_value
  
  return(row)
}

# Apply the custom function to each row
df <- df %>%
  rowwise() %>%
  mutate(
    row_values = list(replace_last_non_na(unlist(select(., -new_col)), new_col))
  ) %>%
  unnest_wider(row_values) %>%
  select(-new_col)

# Print the resulting dataframe
print(df)
761 chars
34 lines