transpose {purrr} R Documentation

## Transpose a list.

### Description

Transpose turns a list-of-lists "inside-out"; it turns a pair of lists into a list of pairs, or a list of pairs into pair of lists. For example, if you had a list of length n where each component had values `a` and `b`, `transpose()` would make a list with elements `a` and `b` that contained lists of length n. It's called transpose because `x[[1]][[2]]` is equivalent to `transpose(x)[[2]][[1]]`.

### Usage

```transpose(.l, .names = NULL)
```

### Arguments

 `.l` A list of vectors to zip. The first element is used as the template; you'll get a warning if a sub-list is not the same length as the first element. `.names` For efficiency, `transpose()` usually inspects the first component of `.l` to determine the structure. Use `.names` if you want to override this default.

### Details

Note that `transpose()` is its own inverse, much like the transpose operation on a matrix. You can get back the original input by transposing it twice.

### Value

A list with indexing transposed compared to `.l`.

### Examples

```x <- rerun(5, x = runif(1), y = runif(5))
x %>% str()
x %>% transpose() %>% str()
# Back to where we started
x %>% transpose() %>% transpose() %>% str()

# transpose() is useful in conjunction with safely() & quietly()
x <- list("a", 1, 2)
y <- x %>% map(safely(log))
y %>% str()
y %>% transpose() %>% str()

# Use simplify_all() to reduce to atomic vectors where possible
x <- list(list(a = 1, b = 2), list(a = 3, b = 4), list(a = 5, b = 6))
x %>% transpose()
x %>% transpose() %>% simplify_all()

# Provide explicit component names to prevent loss of those that don't
# appear in first component
ll <- list(
list(x = 1, y = "one"),
list(z = "deux", x = 2)
)
ll %>% transpose()
nms <- ll %>% map(names) %>% reduce(union)
ll %>% transpose(.names = nms)
```

[Package purrr version 0.2.5 Index]