R help - Sep 2016 - separate commands by semicolon

> On Sep 17, 2016, at 8:28 AM, Adrian Du?a <dusa.adrian at unibuc.ro>
wrote:
> 
> There is one minor problem with parse(): if any of the individual commands
> has an error, the entire text will be parsed in a single error.
> 
> For example, in a normal R console:
> 
>> print(2); ls(
> [1] 2
> +
> 
> So first print(2) is executed, and only after the console expects the user
> to continue the command from ls(
> Parsing the same text:
> 
>> parse(text = "print(2); ls(")
> Error in parse(text = "print(2); ls(") :
>  <text>:2:0: unexpected end of input
> 1: print(2); ls(
>   ^
> 
> What I would need is something to separate the two commands, irrespective
> of their syntactical correctness:
> 
> [1] "print(2)" "ls("
> 
> I hope this explains the situation,
Not entirely clear. If you were intending to just get character output then you
could just use:

strsplit(txt, ";")

If you wanted parsing to an R expression to occur you could pass through sapply
and get a full accounting of the syntactic deficit using `try`:

sapply(strsplit( "print(2); ls(" , ";")[[1]] , function(t)
{try(parse(text=t))})
Error in parse(text = t) : <text>:2:0: unexpected end of input
1:  ls(
   ^
expression(`print(2)` = print(2), ` ls(` = "Error in parse(text = t) :
<text>:2:0: unexpected end of input\n1:  ls(\n   ^\n")

> Adrian
> 
> On Thu, Sep 15, 2016 at 11:02 PM, Adrian Du?a <dusa.adrian at
unibuc.ro> wrote:
> 
>> On Thu, Sep 15, 2016 at 10:28 PM, William Dunlap <wdunlap at
tibco.com>
>> wrote:
>> 
>>> The most reliable way to split such lines is with parse(text=x).
>>> Regular expressions don't do well with context-free grammars.
>>> 
>> 
>> Oh, that's right of course.
>>> as.character(parse(text = x))
>> [1] "foo <- \"3;4\""                   
"bar <- \"don't ; use semicolons\""
>> 
>> That was simple enough, thanks very much,
>> Adrian
>> 
>> --
>> Adrian Dusa
>> University of Bucharest
>> Romanian Social Data Archive
>> Soseaua Panduri nr.90
>> 050663 Bucharest sector 5
>> Romania
>> 
> 
> 
> 
> -- 
> Adrian Dusa
> University of Bucharest
> Romanian Social Data Archive
> Soseaua Panduri nr.90
> 050663 Bucharest sector 5
> Romania
> 
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> 
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David Winsemius
Alameda, CA, USA

On Sat, Sep 17, 2016 at 2:12 PM, David Winsemius <dwinsemius at
comcast.net> wrote:
>
>
> Not entirely clear. If you were intending to just get character output then
you could just use:
>
> strsplit(txt, ";")
>
> If you wanted parsing to an R expression to occur you could pass through
sapply and get a full accounting of the syntactic deficit using `try`:
>
> sapply(strsplit( "print(2); ls(" , ";")[[1]] ,
function(t) {try(parse(text=t))})
> Error in parse(text = t) : <text>:2:0: unexpected end of input
> 1:  ls(
>    ^
> expression(`print(2)` = print(2), ` ls(` = "Error in parse(text = t) :
<text>:2:0: unexpected end of input\n1:  ls(\n   ^\n")
>
You would want to avoid splitting within character strings
(print(";")) and in comments (print(2); ls() # This prints 2; then
lists...) The comment char could also appear in a character string,
where it does not mean the start of a comment...

Not sure how to accomplish that using strsplit (or in general using
just regular expressions).

Peter

On Sun, Sep 18, 2016 at 12:34 AM, Peter Langfelder <
peter.langfelder at gmail.com> wrote:
> On Sat, Sep 17, 2016 at 2:12 PM, David Winsemius <dwinsemius at
comcast.net>
> wrote:
> > Not entirely clear. If you were intending to just get character output
> then you could just use:
> >
> > strsplit(txt, ";")
>
> You would want to avoid splitting within character strings
> (print(";")) and in comments (print(2); ls() # This prints 2;
then
> lists...) The comment char could also appear in a character string,
> where it does not mean the start of a comment...

Yes, that would be the problem.
Returning to my original post, modifying the example:

x <- "print(2); bar <- \"don't ; use semicolons\"; foo
<- '3;4'; ls("

This should result in a character vector of length 4:
[1] "print(2)"                          "bar <-
\"don't ; use semicolons\""
[3] "foo <- '3;4'"                      "ls("

even though the last command would cause an error using parse(text = x)

Perhaps this is not that important (I am trying to simulate a normal R
console), and parse only if it syntactically correct.
I was merely curious if this could be done, likely using regular
expressions (surely strsplit doesn't solve it).

Best,
Adrian

-- 
Adrian Dusa
University of Bucharest
Romanian Social Data Archive
Soseaua Panduri nr.90
050663 Bucharest sector 5
Romania

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