[ESS] Feature idea: insert expression before <- at point

[Vitalie Spinu]

Hi Sven,

My suggestion would be that instead of cluttering your code with such "old
fashion" assignments you would switch to dplyr mutate or data.table's inline
:=. Both are the de-facto standards in the wild by now.

 Vitalie

>> On Tue, Apr 30 2019 15:28, Alex Branham via ESS-help wrote:

> On Tue 30 Apr 2019 at 13:25, Sven Hartenstein via ESS-help <ess-help using r-project.org> wrote:

>> Dear ESS users and developers,
>>
>> when writing R code to manipulate an object or data frame column, I
>> often find myself retyping the expression on the left side of "<-" as
>> some argument for a function call or assignment on the right side of
>> "<-".
>>
>> Here are two examples. Imagine your point is at _POINT_ and you want to
>> insert 'data[,"columnA"]' in the first example and in the second example
>> 'data[ data[,"columnB"] < 123 ,"columnA"]' at point.
>>
>> data[,"columnA"] <- tolower(_POINT_)
>>
>> data[ data[,"columnB"] > 123 ,"columnA"] <- gsub("xxx",
>>                                                   "yyy",
>>                                                   _POINT_,
>>                                                   fixed=TRUE)
>>
>> Wouldn't it be handy to have a lisp function which copies the expression
>> on the left side of "<-" and inserts it at point?
>>
>> Or is something like this already available in ESS?

> Not to my knowledge, no.

>> What do you think?

> I don't think it's a terrible idea; I've found myself wanting to do that
> several times in the past (though less so now with magrittr pipes).

> I guess implementation-wise the tricky bit would be figuring out what to
> do in the case of 1) more than one assignment e.g. x <- y <- 2 and also
> 2) how to find the start of the "left" side. It would be tricky to
> differentiate between:

> x[[
>   1]] <- 1

> and

> x <- 1
> y <- 2

> since we can't reliably detect complete R, especially not backwards. I
> guess one quick workaround would be to work with indentation --- just to
> take all the lines starting with whitespace before the <- until we find
> one all-whitespace line or the first line that doesn't start with
> whitespace.

> Thanks for the suggestion,
> Alex

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