Hello:
Do you know of a simple function to return the value of a named
element of a list if that exists, and return a default value otherwise?
It's an easy function to write (e.g., below). I plan to add this
to the "Ecfun" package unless I find it in another CRAN package.
Thanks,
Spencer
getElement <- function(element, default, list){
# get element of list; return elDefault if absent
El <- list[[element]]
if(is.null(El)){
El <- default
}
El
}
On Apr 15, 2014, at 10:53 AM, Spencer Graves <spencer.graves at structuremonitoring.com> wrote:> Hello: > > > Do you know of a simple function to return the value of a named element of a list if that exists, and return a default value otherwise? > > > It's an easy function to write (e.g., below). I plan to add this to the "Ecfun" package unless I find it in another CRAN package. > > > Thanks, > Spencer > > > getElement <- function(element, default, list){ > # get element of list; return elDefault if absent > El <- list[[element]] > if(is.null(El)){ > El <- default > } > El > }Hi Spencer, I don't know of a function elsewhere, but you can probably simplify the above with: getElement <- function(element, default, list) { ifelse(is.null(list[[element]]), default, list[[element]]) } MyList <- list(L1 = 1, L2 = 2)> MyList$L1 [1] 1 $L2 [1] 2> getElement("L1", 5, MyList)[1] 1> getElement("L2", 5, MyList)[1] 2> getElement("L3", 5, MyList)[1] 5 You might want to think about the ordering of the function arguments, given typical use, for ease of calling it. For example: getElement <- function(list, element, default = SomeValue) Another consideration is that the above function will only get the element if it is a 'first level' element in the list. If it is in a sub-list of the main list, you would need to think about a recursive approach of some type, along the lines of what ?rapply does. Regards, Marc Schwartz
You really want to use the names of the list since lists can contain
null. I'd recommend something more like:
getElement <- function(x, i, default) {
if (i %in% names(x)) return(x[[i]])
default
}
Hadley
On Tue, Apr 15, 2014 at 10:53 AM, Spencer Graves
<spencer.graves at structuremonitoring.com> wrote:> Hello:
>
>
> Do you know of a simple function to return the value of a named
> element of a list if that exists, and return a default value otherwise?
>
>
> It's an easy function to write (e.g., below). I plan to add this
to
> the "Ecfun" package unless I find it in another CRAN package.
>
>
> Thanks,
> Spencer
>
>
> getElement <- function(element, default, list){
> # get element of list; return elDefault if absent
> El <- list[[element]]
> if(is.null(El)){
> El <- default
> }
> El
> }
>
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