rtibbleunnest

Unnesting tibble after matrix multiplication

As simple example I want to calculate the matrix product of two vectors.

a <- tibble(n=c("A", "B"), y=c(10,20))
b <- tibble(x=c(5, 15))

res <- a %>% 
  mutate(rotated = map2(y, b, ~ .x %*% .y)) %>% 
  unnest(rotated)

Everything seems to be fine, but I would expect, that after unnesting, the tibble should be 2x4 tibble, but I have still a 2x3 tibble, e.g.

  n         y rotated[,1]  [,2]
  <chr> <dbl>       <dbl> <dbl>
1 A        10          50   150
2 B        20         100   300

so after checking

res$rotated

I'll get the error

Error in if (nchar(current) > nchars) { : 
  missing value where TRUE/FALSE needed

Also the answer in

How to unnest tibbles within a tibble?

with bind_colsdoesn't solve the problem.

Thanks for any hints

Solution

  • Probably you can try unnest_wider like below

    a %>%
  mutate(rotated = as.data.frame(do.call(rbind, map2(y, b, ~ .x %*% .y)))) %>%
  unnest_wider(rotated)

    or

    a %>%
  reframe(rotated = as.data.frame(map2(y, b, ~ .x %*% .y)), .by = c(n, y)) %>%
  unnest_wider(rotated)

    which gives

    # A tibble: 2 × 4
  n         y    X1    X2
  <chr> <dbl> <dbl> <dbl>
1 A        10    50   150
2 B        20   100   300