Modifying specified list elements r

Question

I have an output that looks like this:

test_list <- list(list(x = c(10, 101, 3), y = c(9, 12, 11)),
                  list(x = c(10, 133, 4), y = c(9, 15, 13)),
                  list(x = c(10, 101, 90), y = c(9, 18, 11)),
                  list(x = c(10, 101, 1), y = c(9, 10, 15)))

I would like to select and modify specific elements of sublists x and y. For example I would like to replace the last element of x with a number from a vector or generated from a function - i.e; map the vector z <- c(10, 50, 6, 12) over the last element of sublists x to result in:

test_list_1 <- list(list(x = c(10, 101, 10), y = c(9, 12, 11)),
                  list(x = c(10, 133, 50), y = c(9, 15, 13)),
                  list(x = c(10, 101, 6), y = c(9, 18, 11)),
                  list(x = c(10, 101, 12), y = c(9, 10, 15)))

or a function such as rnorm(1) over the last element of each sublist x to result in the output from:

test_list_2 <- list(list(x = c(10, 101, rnorm(1)), y = c(9, 12, 11)),
                    list(x = c(10, 133, rnorm(1)), y = c(9, 15, 13)),
                    list(x = c(10, 101, rnorm(1)), y = c(9, 18, 11)),
                    list(x = c(10, 101, rnorm(1)), y = c(9, 10, 15)))

I have been trying the purrr package but the syntax are new to me.

Attempted:

purrr::map(test_list, ~ .x$x[length(.x$x)]) selects correct list/depth but unable to modify.

purrr::modify_depth(test_list, 2, rnorm(1)) I can see why this selects the incorrect depth but not sure how to correct.

So far I can only find examples of manipulating simple list structures in simple ways or complex examples I have not managed to transfer.

Any help would be much appreciated, overall my attempts seem quite clumsy and difficult to generalise for future use.

Thanks!

Maurits Evers Maurits Evers · Accepted Answer · 2018-07-31T01:52:14

In base R you can use Map.

Example 1

z <- c(10, 50, 6, 12)
Map(function(v, w) { v$x <- replace(v$x, 3, w); v; }, test_list, z)
#[[1]]
#[[1]]$x
#[1]  10 101  10
#
#[[1]]$y
#[1]  9 12 11
#
#
#[[2]]
#[[2]]$x
#[1]  10 133  50
#
#[[2]]$y
#[1]  9 15 13
#
#
#[[3]]
#[[3]]$x
#[1]  10 101   6
#
#[[3]]$y
#[1]  9 18 11
#
#
#[[4]]
#[[4]]$x
#[1]  10 101  12
#
#[[4]]$y
#[1]  9 10 15

Example 2

Map(function(v, w) { v$x <- replace(v$x, 3, w); v; }, test_list, rnorm(length(test_list)))

Or the same using purrr::map2

purrr::map2(test_list, z, function(v, w) { v$x <- replace(v$x, 3, w); v; })
purrr::map2(test_list, rnorm(length(test_list)), function(v, w) { v$x <- replace(v$x, 3, w); v; })

Modifying specified list elements r

1 Answers