Store (almost) all objects in workspace in a list

问题:

Let's say that I have many objects in my workspace (global environment) and I want to store most of those in a list. Here's a simplified example:

# Put some objects in the workspace
A <- 1
B <- 2
C <- 3

I would like to store objects A and C in a list. Of course, I can do that explicitly:

mylist <- list(A,C)

However, when the number of objects in the workspace is very large, this would become rather cumbersome. Hence, I would like to do this differently and attempted the following:

mylist <- list(setdiff(ls(),B))

But this obviously is not what I want, as it only stores the names of the objects in the workspace.

Any suggestions on how I can do this?

Many thanks!

回答1:

Another option is to use mget:

mget(setdiff(ls(),"B"))

回答2:

EDIT : I think using lapply / sapply here raises too many problems. You should definitely use the mget answer.

You can try :

mylist <- sapply(setdiff(ls(),"B"), get)

In certain cases, ie if all the objects in your workspace are of the same type, sapply will return a vector. For example :

sapply(setdiff(ls(),"B"), get)
# A C 
# 1 3 

Otherwise, it will return a list :

v <- list(1:2)
sapply(setdiff(ls(),"B"), get)
# $A
# [1] 1
# 
# $C
# [1] 3
# 
# $v
# [1] 1 2

So using lapply instead of sapply here could be safer, as Josh O'Brien pointed out.

回答3:

mget is definitely the easiest to use in this situation. However, you can achieve the same with as.list.environment and eapply:

e2l <- as.list(.GlobalEnv)
# or: e2l <- as.list(environment()) 
# using environment() within a function returns the function's env rather than .GlobalEnv
e2l[! names(e2l) %in "B"]

# the following one sounds particularly manly with `force`
e2l <- eapply(environment(), force)
e2l[! names(e2l) %in "B"]

And one-liners:

 (function(x) x[!names(x)%in%"B"])(eapply(environment(), force))
 (function(x) x[!names(x)%in%"B"])(as.list(environment()))