```
# unnest() is designed to work with lists of data frames
df <- tibble(
x = 1:3,
y = list(
NULL,
tibble(a = 1, b = 2),
tibble(a = 1:3, b = 3:1, c = 4)
)
)
# unnest() recycles input rows for each row of the list-column
# and adds a column for each column
df %>% unnest(y)
# input rows with 0 rows in the list-column will usually disappear,
# but you can keep them (generating NAs) with keep_empty = TRUE:
df %>% unnest(y, keep_empty = TRUE)
# Multiple columns ----------------------------------------------------------
# You can unnest multiple columns simultaneously
df <- tibble(
x = 1:2,
y = list(
tibble(a = 1, b = 2),
tibble(a = 3:4, b = 5:6)
),
z = list(
tibble(c = 1, d = 2),
tibble(c = 3:4, d = 5:6)
)
)
df %>% unnest(c(y, z))
# Compare with unnesting one column at a time, which generates
# the Cartesian product
df %>%
unnest(y) %>%
unnest(z)
```

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