thr3ads.net - R help - [R] Antwort: Re: Accessing an object using a string [Aug 2016]

If this information is useful, please help other people find it:
Share via:

G.Maubach at weinwolf.de

2016-Aug-15 08:49 UTC

[R] Accessing an object using a string

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

G.Maubach at weinwolf.de

2016-Aug-15 13:40 UTC

head link

[R] Antwort: Accessing an object using a string (SOLVED)

Hi All,

I found the function get() which returns an object.

My whole function looks like this:

-- cut --

#-------------------------------------------------------------------------------
# Module        : t_load_dataset.R
# Author        : Georg Maubach
# Date          : 2016-08-15
# Update        : 2016-08-15
# Description   : Load dataset and print information on contents
# Source System : R 3.3.0 (64 Bit)
# Target System : R 3.3.0 (64 Bit)
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#--------1---------2---------3---------4---------5---------6---------7---------8

t_module_name = "t_load_dataset"
t_version = "2016-08-15"
t_status = "released"

cat(
  paste0("\n",
         t_module_name, " (Version: ", t_version, ", Status:
", t_status,
")", "\n", "\n",
         "Copyright (C) Georg Maubach 2016

This software comes with ABSOLUTELY NO WARRANTY.", "\n",
"\n"))

# If do_test is not defined globally define it here locally by 
un-commenting it
# Switch t_do_test to TRUE to run test
t_do_test <- FALSE

# [ Function Defintion 
]--------------------------------------------------------
t_load_dataset <- function(file_path,
                           file_name) {
  # Loads and RData file with all objects in it and prints information on 
its
  # contents
  #
  # Args:
  #  file_path (string):
  #    String with path name.
  #  file_name (string):
  #    String with file name.
  #
  # Operation:
  #   Loads the RData file with all its objects, stores the objects in the
  #   global environment .GlobalEnv and prints information about the 
objects.
  #
  # Usage:
  #   The function is designed to work only on data frames.
  #
  # Returns:
  #   Nothing, but stores loaded objects directly into the global 
environment.
  #
  # Error handling:
  #   None.
 
#-----------------------------------------------------------------------------
 
  cat("----------------------- [ t_load_dataset() ] 
----------------------\n\n")
 
  file_location <- file.path(file_path, file_name)
 
  cat(paste0('Loading ', file_location, " ...\n\n"))
 
  dataset_list <- load(file = file_location,
                       envir = .GlobalEnv)
 
  cat(paste0(
    length(dataset_list),
    " dataset(s) loaded:\n"))
  cat(dataset_list)
  cat("\n\n")

  for (dataset in dataset_list) {
    cat(paste0("Dataset '", dataset, "' contains ",
                nrow(get(dataset, envir = .GlobalEnv)),
                " cases in ",
                ncol(get(dataset, envir = .GlobalEnv)),
                " variables:\n"))
    cat(names(get(dataset, envir = .GlobalEnv)))
    cat("\n\n")
  }
 
  cat("------------------------------ [ Done ] 
---------------------------\n\n")
}

# [ Test Defintion 
]------------------------------------------------------------
t_test <- function(do_test = FALSE) {
  if (do_test == TRUE) {
 
    # Example dataset
    var1 <- c(1, 2, 3)
    var2 <- c(4, 5, 6)
    d_data1 <- data.frame(var1, var2)
 
    var3 <- c(7, 8, 9)
    var4 <- c(10, 11, 12)
    d_data2 <- data.frame(var3, var4)
 
    # Save datasets
    v_file_name <- "test_t_load_dataset.RData"
 
    save(file = file.path(getwd(),
                          v_file_name),
         list = c("d_data1", "d_data2"))
 
    # Call function
    t_load_dataset(file_path = getwd(), file_name = v_file_name)
 
    # Cleanup
    unlink(file.path(getwd(), v_file_name))
  }
}

# [ Test Run 
]------------------------------------------------------------------
t_test(do_test = t_do_test)

# [ Clean up 
]------------------------------------------------------------------
rm("t_module_name", "t_version", "t_status",
"t_do_test", "t_test")

# EOF

-- cut --

I will include it later the toolbox of R function on Sourceforge.net.

Kind regards

Georg




Von:    G.Maubach at weinwolf.de
An:     r-help at r-project.org, 
Datum:  15.08.2016 10:51
Betreff:        [R] Accessing an object using a string
Gesendet von:   "R-help" <r-help-bounces at r-project.org>



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.

Jeff Newmiller

2016-Aug-15 16:41 UTC

head link

[R] Antwort: Accessing an object using a string (SOLVED)

Use of "get" usually means you are doing something wrong in setting up
your approach to a problem. That is, if you design your interface to your
functions to be overly general,  it will become full of surprises later.

If in fact the data you are interested in referring to is a column in a data
frame, then let the user give your function that data frame as a function
argument and use indexing to extract the value from it. Don't design your
function to go digging around in the global environment because the user of your
function may not be working there.

In this case, it would be better for the user to create a dedicated environment
and load the RData file into that and use the ls() and str () functions to look
through it rather than assume the RData file only contains data frames by using
your function.

x <- 1:5
dta <- data.frame( x, y = x + 1 )
save.image( "test.RData" )
rm( x )
rm( dta )
en <- new.env()
ls()
ls( en )
load( "test.RData", envir=en )
ls( en )
str( x ) # removed from working environment
str( en$x )
str( en$dta )

-- 
Sent from my phone. Please excuse my brevity.

On August 15, 2016 6:40:58 AM PDT, G.Maubach at weinwolf.de
wrote:>Hi All,
>
>I found the function get() which returns an object.
>
>My whole function looks like this:
>
>-- cut --
>
>#-------------------------------------------------------------------------------
># Module        : t_load_dataset.R
># Author        : Georg Maubach
># Date          : 2016-08-15
># Update        : 2016-08-15
># Description   : Load dataset and print information on contents
># Source System : R 3.3.0 (64 Bit)
># Target System : R 3.3.0 (64 Bit)
>#
># This program is distributed in the hope that it will be useful,
># but WITHOUT ANY WARRANTY; without even the implied warranty of
># MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>#--------1---------2---------3---------4---------5---------6---------7---------8
>
>t_module_name = "t_load_dataset"
>t_version = "2016-08-15"
>t_status = "released"
>
>cat(
>  paste0("\n",
>      t_module_name, " (Version: ", t_version, ", Status:
", t_status,
>")", "\n", "\n",
>         "Copyright (C) Georg Maubach 2016
>
>This software comes with ABSOLUTELY NO WARRANTY.", "\n",
"\n"))
>
># If do_test is not defined globally define it here locally by 
>un-commenting it
># Switch t_do_test to TRUE to run test
>t_do_test <- FALSE
>
># [ Function Defintion 
>]--------------------------------------------------------
>t_load_dataset <- function(file_path,
>                           file_name) {
># Loads and RData file with all objects in it and prints information on
>
>its
>  # contents
>  #
>  # Args:
>  #  file_path (string):
>  #    String with path name.
>  #  file_name (string):
>  #    String with file name.
>  #
>  # Operation:
>#   Loads the RData file with all its objects, stores the objects in
>the
>  #   global environment .GlobalEnv and prints information about the 
>objects.
>  #
>  # Usage:
>  #   The function is designed to work only on data frames.
>  #
>  # Returns:
>  #   Nothing, but stores loaded objects directly into the global 
>environment.
>  #
>  # Error handling:
>  #   None.
> 
>#-----------------------------------------------------------------------------
> 
>  cat("----------------------- [ t_load_dataset() ] 
>----------------------\n\n")
> 
>  file_location <- file.path(file_path, file_name)
> 
>  cat(paste0('Loading ', file_location, " ...\n\n"))
> 
>  dataset_list <- load(file = file_location,
>                       envir = .GlobalEnv)
> 
>  cat(paste0(
>    length(dataset_list),
>    " dataset(s) loaded:\n"))
>  cat(dataset_list)
>  cat("\n\n")
>
>  for (dataset in dataset_list) {
>    cat(paste0("Dataset '", dataset, "' contains
",
>                nrow(get(dataset, envir = .GlobalEnv)),
>                " cases in ",
>                ncol(get(dataset, envir = .GlobalEnv)),
>                " variables:\n"))
>    cat(names(get(dataset, envir = .GlobalEnv)))
>    cat("\n\n")
>  }
> 
>  cat("------------------------------ [ Done ] 
>---------------------------\n\n")
>}
>
># [ Test Defintion 
>]------------------------------------------------------------
>t_test <- function(do_test = FALSE) {
>  if (do_test == TRUE) {
> 
>    # Example dataset
>    var1 <- c(1, 2, 3)
>    var2 <- c(4, 5, 6)
>    d_data1 <- data.frame(var1, var2)
> 
>    var3 <- c(7, 8, 9)
>    var4 <- c(10, 11, 12)
>    d_data2 <- data.frame(var3, var4)
> 
>    # Save datasets
>    v_file_name <- "test_t_load_dataset.RData"
> 
>    save(file = file.path(getwd(),
>                          v_file_name),
>         list = c("d_data1", "d_data2"))
> 
>    # Call function
>    t_load_dataset(file_path = getwd(), file_name = v_file_name)
> 
>    # Cleanup
>    unlink(file.path(getwd(), v_file_name))
>  }
>}
>
># [ Test Run 
>]------------------------------------------------------------------
>t_test(do_test = t_do_test)
>
># [ Clean up 
>]------------------------------------------------------------------
>rm("t_module_name", "t_version", "t_status",
"t_do_test", "t_test")
>
># EOF
>
>-- cut --
>
>I will include it later the toolbox of R function on Sourceforge.net.
>
>Kind regards
>
>Georg
>
>
>
>
>Von:    G.Maubach at weinwolf.de
>An:     r-help at r-project.org, 
>Datum:  15.08.2016 10:51
>Betreff:        [R] Accessing an object using a string
>Gesendet von:   "R-help" <r-help-bounces at r-project.org>
>
>
>
>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.
>
>______________________________________________
>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.

Greg Snow

2016-Aug-15 18:33 UTC

head link

[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

William Dunlap

2016-Aug-15 19:10 UTC

head link

[R] Accessing an object using a string

'names' is an S3-generic function.  E.g., in R-3.3.0:

  > names.unnamed <- function(x) sprintf("#%0*d",
ceiling(log10(length(x))), seq_along(x))
  > u <- structure(letters, class="unnamed")
  > names(u)
   [1] "#01" "#02" "#03" "#04"
"#05" "#06" "#07"
   [8] "#08" "#09" "#10" "#11"
"#12" "#13" "#14"
  [15] "#15" "#16" "#17" "#18"
"#19" "#20" "#21"
  [22] "#22" "#23" "#24" "#25"
"#26"

There are a lot of C/C++ based functions that use an internal function to
get
the names of vectors and they may not use this method, but R code will use
it.


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Aug 15, 2016 at 11:33 AM, Greg Snow <538280 at gmail.com> wrote:
> 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
>
> ______________________________________________
> 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.
>
	[[alternative HTML version deleted]]

G.Maubach at weinwolf.de

2016-Aug-16 06:43 UTC

head link

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

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
>
> ______________________________________________
> 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

R help - Aug 2016 - Antwort: Re: Accessing an object using a string

[R] Accessing an object using a string

[R] Antwort: Accessing an object using a string (SOLVED)

[R] Antwort: Accessing an object using a string (SOLVED)

[R] Accessing an object using a string

[R] Accessing an object using a string

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