[R] Antwort: Re: Accessing an object using a string

[G.Maubach at weinwolf.de]

Hi Greg 
and all others who replied to my question,

many thanks for all your answers and help. Currently I store all my 
objects in .GlobalEnv = Workspace. I am not yet familiar working with 
different environments nor did I see that this would be necessary for my 
analysis.

Could you explain why working with different environments would be 
helpful?

You suggested to read variables into lists rather than storing them in 
global variables. This sounds interesting. Could you provide an example of 
how to define and use this?

Kind regards

Georg



Von:    Greg Snow <538280 at gmail.com>
An:     G.Maubach at weinwolf.de, 
Kopie:  r-help <r-help at r-project.org>
Datum:  15.08.2016 20:33
Betreff:        Re: [R] Accessing an object using a string



The names function is a primitive, which means that if it does not
already do what you want, it is generally not going to be easy to
coerce it to do it.

However, the names of an object are generally stored as an attribute
of that object, which can be accessed using the attr or attributes
functions.  If you change your code to not use the names function and
instead use attr or attributes to access the names then it should work
for you.


You may also want to consider changing your workflow to have your data
objects read into a list rather than global variables, then process
using lapply/sapply (this would require a change in how your data is
saved from your example, but if you can change that then everything
after can be cleaner/simpler/easier/more fool proof/etc.)


On Mon, Aug 15, 2016 at 2:49 AM,  <G.Maubach at weinwolf.de> wrote:
> Hi All,
>
> I would like to access an object using a sting.
>
> # Create example dataset
> var1 <- c(1, 2, 3)
> var2 <- c(4, 5, 6)
> data1 <- data.frame(var1, var2)
>
> var3 <- c(7, 8, 9)
> var4 <- c(10, 11, 12)
> data2 <- data.frame(var3, var4)
>
> save(file = "c:/temp/test.RData", list = c("data1", "data2"))
>
> # Define function
> t_load_dataset <- function(file_path,
>                            file_name) {
>   file_location <- file.path(file_path, file_name)
>
>   print(paste0('Loading ', file_location, " ..."))
>   cat("\n")
>
>   object_list <- load(file = file_location,
>                       envir = .GlobalEnv)
>
>   print(paste(length(object_list), "dataset(s) loaded from",
> file_location))
>   cat("\n")
>
>   print("The following objects were loaded:")
>   print(object_list)
>   cat("\n")
>
>   for (i in object_list) {
>     print(paste0("Object '", i, "' in '", file_name, "' contains:"))
>     str(i)
>     names(i)  # does not work
>   }
> }
>
> I have only the character vector object_list containing the names of the
> objects as strings. I would like to access the objects in object_list to
> be able to print the names of the variables within the object (usuallly 
a
> data frame).
>
> Is it possible to do this? How is it done?
>
> Kind regards
>
> Georg
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com