Assigning names to the list output of dplyr do operation

Question

The do function in the package dplyr usually produces the list. Is there are way to assign names to that list depending on the input to d

Answer 1

You can create a data.frame within your function:

 mods <- do(group_by(it,ind),function(x)
        data.frame(it=unique(as.character(x$ind)),val=min(x$var1)))

Then :

do.call(rbind,mods)
  it val
1  a   1
2  b   3
3  c   5

EDIT

 mods <- do(group_by(it,ind),
      function(x) setNames(list(min(x$var1)),unique(as.character(x$ind))))

unlist(mods,rec=FALSE)
$a
[1] 1

$b
[1] 3

$c
[1] 5

Answer 2

Try this marked up version of do.grouped_df:

do2 <- function (.data, .f, ...) {
    if (is.null(attr(.data, "indices"))) {
        .data <- dplyr:::grouped_df_impl(.data, attr(.data, "vars"), 
            attr(.data, "drop"))
    }
    index <- attr(.data, "indices")
    out <- vector("list", length(index))
    for (i in seq_along(index)) {
        subs <- .data[index[[i]] + 1L, , drop = FALSE]
        out[[i]] <- .f(subs, ...)
    }
    nms <- as.character(attr(.data, "labels")[[1]])
    setNames(out, nms)
}

library(gusbfn)

it %.% group_by(ind) %.% do2(function(x) min(x$var1))

which gives:

$a
[1] 1

$b
[1] 3

$c
[1] 5

It could also be combined with fn$ from the gsubfn package like this to shorten it slightly:

library(dplyr)
library(gsubfn)

it %.% group_by(ind) %.% fn$do2(~ min(x$var1))

giving the same answer.