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 do
? Specifically I pass the group_by
result and would like that the names of the list would give some indication to what group the list elements correspond.
Here is the toy example of what I want to achieve:
> it = data.frame(ind=c("a","a","b","b","c"),var1=c(1,2,3,4,5), var1=c(2,3,4,2,2))
> group_by(it,ind)%.%summarise(min(var1))
Source: local data frame [3 x 2]
ind min(var1)
1 c 5
2 b 3
3 a 1
Now do this with do
> do(group_by(it,ind),function(x)min(x[,"var1"]))
[[1]]
[1] 5
[[2]]
[1] 3
[[3]]
[1] 1
Ideally the names should be c("c","b","a")
.
Is this possible? And why dplyr reverses sorting of the groups? Note in my case the result of the do
operation is a lm
object.
Edit: The comment asks for realistic example, here is what I had in mind. I fit models depending on the data (dummy code):
res <- do(group_by(data,Index),lm,formula=y~x)
Now I want to do various things like
sapply(res,coef)
So I want to relate the results to the original dataset, in this case to what Index
the coefficients correspond.
Edit 2: The desired behaviour can be achieved with dlply
function:
dlply(it,~ind,function(d)min(d[,"var1"]))
$a
[1] 1
$b
[1] 3
$c
[1] 5
attr(,"split_type")
[1] "data.frame"
attr(,"split_labels")
ind
1 a
2 b
3 c
I am looking whether it is possible to replicate this behaviour with dplyr, preferably with minimal intervention.
Try this marked up version of do.grouped_df
:
do2 <- function (.data, .f, ...) {
if (is.null(attr(.data, "indices"))) {
.data <- dplyr:::grouped_df_impl(.data, attr(.data, "vars"),
attr(.data, "drop"))
}
index <- attr(.data, "indices")
out <- vector("list", length(index))
for (i in seq_along(index)) {
subs <- .data[index[[i]] + 1L, , drop = FALSE]
out[[i]] <- .f(subs, ...)
}
nms <- as.character(attr(.data, "labels")[[1]])
setNames(out, nms)
}
library(gusbfn)
it %.% group_by(ind) %.% do2(function(x) min(x$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.
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