Q:

tidyr reshape tibble without expand.grid

I'd like to reshape a tibble without using expand.grid. While expand.grid + delete missing obs + delete "flipped duplicates" (i.e a,b is the same as b,a) shall work, it would be quite slow to compute provided the many combinations I have.
This is a dummy version of what I want to achieve:
library(dplyr)
library(tidyr)

initial_data <- tibble(x = c("east","east","east"), y = c("a","b","c"), z = c(0.1,0.2,0.3))

> initial_data
# A tibble: 3 x 3
      x     y     z
  <chr> <chr> <dbl>
1  east     a   0.1
2  east     b   0.2
3  east     c   0.3

final_data <- tibble(x = c("east","east","east"), y1 = c("a","a","b"), y2 = c("b","c","c"), z1 = c(0.1,0.1,0.2), z2 = c(0.2,0.3,0.3))

> final_data
# A tibble: 3 x 5
      x    y1    y2    z1    z2
  <chr> <chr> <chr> <dbl> <dbl>
1  east     a     b   0.1   0.2
2  east     a     c   0.1   0.3
3  east     b     c   0.2   0.3

This works but is extremely inefficient:
expand_data <- as_tibble(expand.grid(initial_data$x, initial_data$y, initial_data$y)) %>% 
  filter(Var2 != Var3) %>% 
  distinct()

index <- !duplicated(t(apply(expand_data, 1, sort)))
expand_data <- expand_data[index, ] %>% 
  left_join(initial_data, by = c("Var1" = "x", "Var2" = "y")) %>% 
  left_join(initial_data, by = c("Var1" = "x", "Var3" = "y"))

> expand_data
# A tibble: 3 x 5
   Var1  Var2  Var3   z.x   z.y
  <chr> <chr> <chr> <dbl> <dbl>
1  east     b     a   0.2   0.1
2  east     c     a   0.3   0.1
3  east     c     b   0.3   0.2

Many thanks in advance !!

A:

What about do a inner join and then filter for unique combinations?
library(dplyr)
inner_join(initial_data, initial_data,
           suffix = c('1', '2'), by = 'x') %>%
    filter(y1 < y2) %>%
    select(x, y1, y2, z1, z2)

#      x y1 y2  z1  z2
# 1 east  a  b 0.1 0.2
# 2 east  a  c 0.1 0.3
# 3 east  b  c 0.2 0.3

