purrr (version 0.1.0)

at_depth: Map a function over lower levels of a nested list

Description

at_depth() maps a function on lower levels of nested lists. In essence, at_depth() is a recursive map.

Usage

at_depth(.x, .depth, .f, ...)

Arguments

.x

A deep list

.depth

Level of .x to map on.

.f

A function, formula or string.

If a function, it is used as is.

If a formula, e.g. ~ .x + 2, it is converted to a function with a three arguments, .x or ., .y, .z. This allows you

...

Additional arguments passed on to .f.

Details

• x %>% at_depth(0, fun)is equivalent tofun(x).
• x %>% at_depth(1, fun)is equivalent tomap(x, fun).
• x %>% at_depth(2, fun)is equivalent tomap(x, . %>% map(fun)).

Examples

l1 <- list(
  obj1 = list(
    prop1 = list(param1 = 1:2, param2 = 3:4),
    prop2 = list(param1 = 5:6, param2 = 7:8)
  ),
  obj2 = list(
    prop1 = list(param1 = 9:10, param2 = 11:12),
    prop2 = list(param1 = 13:14, param2 = 15:16)
  )
)

# In the above list, "obj" is level 1, "prop" is level 2 and "param"
# is level 3. To apply sum() on all params, we map it at depth 3:
l1 %>% at_depth(3, sum)

# map() lets us pluck the elements prop1/param2 in obj1 and obj2:
l1 %>% map(c("prop1", "param2")) %>% str()

# But what if we want to pluck all param2 elements? Then we need to
# act at a lower level:
l1 %>% at_depth(2, "param2") %>% str()


# at_depth can be used in a complementary way with other purrr
# functions to make them operate at a lower level
l2 <- list(
  obj1 = list(
    prop1 = list(c(1, 2), c(3, 4), c(5, 6)),
    prop2 = list(c("a", "b"), c("c", "d"), c("e", "f"))
  ),
  obj2 = list(
    prop1 = list(c(10, 20), c(30, 40), c(50, 60)),
    prop2 = list(c("A", "B"), c("C", "D"), c("E", "F"))
  )
)

# Here we ask map_n() to map paste() simultaneously over all
# elements of the objects at the second level. paste() is thus
# effectively mapped at level 3.
l2 %>% at_depth(2, map_n, paste, sep = "/ ")