attach() inside function

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I'd like to give a params argument to a function and then attach it so that I can use a instead of params$a everytime I refer to the list element a.

run.simulation<-function(model,params){
attach(params)
#
# Use elements of params as parameters in a simulation
detach(params)
}

Is there a problem with this? If I have defined a global variable named c and have also defined an element named c of the list "params" , whose value would be used after the attach command?

Noah has already pointed out that using attach is a bad idea, even though you see it in some examples and books. There is a way around. You can use "local attach" that's called with. In Noah's dummy example, this would look like

with(params, print(a))

which will yield identical result, but is tidier.

attach function, integer specifying position in search() where to attach. name. name to use for the attached database. Names starting with package: are reserved for library . In interactive use, with is usually preferable to the use of attach/detach, unless what is a save()-produced file in which case attach() is a (safety) wrapper for load(). In programming, functions should not change the search path unless that is their purpose. Often with can be used within a function. If not, good practice is to

Another possibility is:

run.simulation <- function(model, params){
    # Assume params is a list of parameters from 
    # "params <- list(name1=value1, name2=value2, etc.)"
    for (v in 1:length(params)) assign(names(params)[v], params[[v]])
    # Use elements of params as parameters in a simulation
}

Attach Set of R Objects to Search Path, integer specifying position in search() where to attach. name When evaluating a variable or function name R searches for that name in the databases listed by  The attach () function in R can be used to make objects within dataframes accessible in R with fewer keystrokes.

Easiest way to solve scope problems like this is usually to try something simple out:

a = 1
params = c()
params$a = 2
myfun <- function(params) {
  attach(params)
  print(a)
  detach(params)
}
myfun(params)

The following object(s) are masked _by_ .GlobalEnv:

a

# [1] 1

As you can see, R is picking up the global attribute a here.

It's almost always a good idea to avoid using attach and detach wherever possible -- scope ends up being tricky to handle (incidentally, it's also best to avoid naming variables c -- R will often figure out what you're referring to, but there are so many other letters out there, why risk it?). In addition, I find code using attach/detach almost impossible to decipher.

[R] be careful: using attach in R functions, So be careful when you use attach in a function! numeric(n) > for(i in seq(n)){ > timeu[i] <- > system.time({ > resi <- f() > })[3] > } > plot(timeu)  The attach function allows to access variables of a data.frame without calling the data.frame. The detach function can be used to: Remove the attachment of a data.frame, which was previously attached with the attach function. Unload a package, which was previously loaded with the library function.

Jean-Luc's answer helped me immensely for a case that I had a data.frame Dat instead of the list as specified in the OP:

for (v in 1:ncol(Dat)) assign(names(Dat)[v], Dat[,v])

To attach() or not attach(): that is the question, The attach() function in R can be used to make objects within The search() function can be used to list attached objects and packages. Table 2: Data After Applying within() Function in R. As Table 2 shows: We just created a new data frame which contains our original data AND a new variable x3. Alternatives to with & within. R provides numerous functions for the handling of data. Similar functions to with and within are, e.g., attach & detach or transform.

attach & detach Functions in R, exampleTwo = { attach: function (context, settings) { $('.example-link', context).​click(function ()  Inside the attached function, delay () won’t work and the value returned by millis () will not increment. Serial data received while in the function may be lost. You should declare as volatile any variables that you modify within the attached function. See the section on ISRs below for more information.

Call a drupal behavior method from inside another behavior, You need to use the once() function to achieve this. someThing = { attach: function (context) { if (context === document) { console.log('called inside'); // Once​  If you execute attach (data) multiple time, eg, 5 times, then you can see (with the help of search ()) that your data has been attached 5 times in the workspace environment. So if you de-attach (detach (data)) it once, there'll still be data present 4 times in the environment. Hence, with ()/within () are better options.

How to prevent behavior-attached functions from being attached , Add the environment for the rquser schema to the R search path. ore.attach() # Create an unordered ore.frame proxy object in the SH environment for the  You can use attachments to store several files in a single field, and you can even store multiple types of files in that field. For example, let's say you own a job contacts database. You can now attach one or more resumes to the record for each contact, plus a photo of each contact.

Comments
  • +1 Worth explaining what with() and within() do. In the example given, with() creates an environment from params and then evaluates the expression print(a) inside that environment. Hence the components of params are visible when the expression is evaluated, without needing to attach() them.
  • Thank you very much for the lucid answers.
  • So what worked in the end was 'myFun <-function(model,params){with(params),{...}}' where ... is the function body