[R] Accessing an object using a string

[Bert Gunter]

Inline.

Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Mon, Aug 15, 2016 at 11:43 PM,  <G.Maubach at weinwolf.de> wrote:
> 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?


It sounds to me as if you really need to spend some time with an R
tutorial or two before you do anything else. There are many good ones
on the web. See here for some suggestions:

https://www.rstudio.com/online-learning/#R

While you may reasonably expect some help with R programming and
related matters here, you should not expect this list to do your
homework for you, at least IMHO (others may disagree).

Cheers,
Bert


>
> 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
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Gregory (Greg) L. Snow Ph.D.
> 538280 at gmail.com
>
>