R: "stack" columns on top of each other

Question

Suppose I have some data like this:

library(dplyr)

a = data.frame( "col" = c("red", "red", "green"), "coll" = c("blue", "blue", "yellow"))

I am trying to take all unique values from "a" and put them into a new frame:

final = data.frame("col" = c("red", "green", "blue", "yellow")

I tried the following approach:

first_col = a %>% distinct(col)
second_col = a %>% distinct(coll)

final = cbind(first_col, second_col)

But this does not seem to be correct.

Could someone please show me what I am doing wrong?

Thanks

user_12158757 · Answer

You can use union with Reduce to make it

> data.frame(a = Reduce(union, a))
       a
1    red
2  green
3   blue
4 yellow

user_3962914 · Answer

You could unlist the dataframe into vector and get unique values from it.

final <- data.frame(col = unique(unlist(a)))
final
#     col
#1    red
#2  green
#3   blue
#4 yellow

A general tidyverse solution would be to get data in long format and get distinct values.

library(dplyr)
library(tidyr)

a %>%
  pivot_longer(cols = everything()) %>%
  distinct(value)

user_3732271 · Answer

We can convert to matrix and then concatenate to a vector with c

data.frame(col = unique(c(as.matrix(a))))