Re: [R] R multiline expression grief
This is a perfectly legal expression:
f - a
+ b
+ c;
Type it in a the console, and it will assign a to f and then print out
the values of b and c. In parsing 'f - a' that is a complete
expression. You may be confused since you think that semicolons
terminate an expression; that is not the case in R. If you write 'f
- a +' and then continue on the next line, R recognizes that the
parsing of the expression is not complete and will continue looking.
So it is not a bug; just a misunderstanding of what the syntax is and
how it works.
There are similar questions when people type in the following type of
statements:
if (1 == 1) print (TRUE)
else print (FALSE)
At the console you get:
if (1 == 1) print (TRUE)
[1] TRUE
else print (FALSE)
Error: unexpected 'else' in else
No suitable frames for recover()
because the parsing of the 'if' is complete. Instead you should be doing:
if (1 == 1) {print (TRUE)
+ } else {print (FALSE)}
[1] TRUE
so the parse knows that the initial 'if' is not complete on the single line.
On Fri, Mar 13, 2009 at 8:55 AM, Paul Suckling paul.suckl...@gmail.com wrote:
Dear all.
After much grief I have finally found the source of some weird
discrepancies in results generated using R. It turns out that this is
due to the way R handles multi-line expressions. Here is an example
with R version 2.8.1:
# R-script...
r_parse_error - function ()
{
a - 1;
b - 1;
c - 1;
d - a + b + c;
e - a +
b +
c;
f - a
+ b
+ c;
cat('a',a,\n);
cat('b',b,\n);
cat('c',c,\n);
cat('d',d,\n);
cat('e',e,\n);
cat('f',f,\n);
}
r_parse_error();
a 1
b 1
c 1
d 3
e 3
f 1
As far as I am concerned f should have the value 3.
This is causing me endless problems since case f is our house style
for breaking up expressions for readability. All our code will need to
be rechecked as a result. Is this behaviour a bug? If not, is it
possible to get R to generate a warning that several lines of an
expression are potentially being ignored, perhaps by turning on a
strict mode which requires the semi-colons?
Thank you,
Paul
__
R-help@r-project.org mailing list
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.
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem that you are trying to solve?
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
On Fri, 13 Mar 2009, Paul Suckling wrote:
Dear all.
After much grief I have finally found the source of some weird
discrepancies in results generated using R. It turns out that this is
due to the way R handles multi-line expressions. Here is an example
with R version 2.8.1:
# R-script...
r_parse_error - function ()
{
a - 1;
b - 1;
c - 1;
d - a + b + c;
e - a +
b +
c;
f - a
+ b
+ c;
cat('a',a,\n);
cat('b',b,\n);
cat('c',c,\n);
cat('d',d,\n);
cat('e',e,\n);
cat('f',f,\n);
}
r_parse_error();
a 1
b 1
c 1
d 3
e 3
f 1
As far as I am concerned f should have the value 3.
That is most unfortunate for you.
Is this behaviour a bug?
No.
If not, is it
possible to get R to generate a warning that several lines of an
expression are potentially being ignored, perhaps by turning on a
strict mode which requires the semi-colons?
No.
R is not ignoring several lines of an expression.
f - a
+ b
+ c;
is three perfectly legitimate expressions over three lines. R evaluates
f-a
then evaluates
+b
then evaluates
+c
For people who like semicolons, it's the same as if you had
f - a;
+b;
+c;
The semicolons are just an alternative to a newline, so a semicolon at the end
of a line is purely cosmetic. Modifying the parser to require a semicolon to
terminate a statement would break essentially every piece of R code and
documentation in existence, so it's probably easier to change your house style.
You could fairly easily write a tool that parsed your scripts and checked that
all your expressions were either assignments or function calls and that the
top-level expressions did not include unary plus or minus.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
tlum...@u.washington.eduUniversity of Washington, Seattle
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
Paul Suckling wrote:
...
# R-script...
r_parse_error - function ()
{
...
f - a
+ b
+ c;
}
...
f 1
As far as I am concerned f should have the value 3.
as far as you intend, perhaps. note, the above snippet says:
f - a; +b; +c
not
f - a + b + c
This is causing me endless problems since case f is our house style
for breaking up expressions for readability. All our code will need to
be rechecked as a result. Is this behaviour a bug?
clearly not. and it's hardly idiosyncratic to r. you'd have the same
behaviour in, e.g., python, though there you can explicitly demand that
the lines form a single statement by ending the first two with a
backslash. there have been similar discussions on mailing lists of a
number of programming/scripting languages.
If not, is it
possible to get R to generate a warning that several lines of an
expression are potentially being ignored,
they're not ignored! you demand to compute +b and +c, and it's
certainly done. (i don't think r is smart enough to optimize these away).
perhaps by turning on a
strict mode which requires the semi-colons?
that's an idea, but the proposed solution would have to be optional to
avoid annoying those who don't like semiquotes in r code.
vQ
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
I get it. Thanks everyone for the feedback.
Now that I understand how it works, my comment would be that this
system is dangerous since it makes it difficult to read the code and
easy to make errors when typing it. I recognise that this is something
so fundamental that it is unlikely to be changed so I'll have to adapt
to it.
My feeling is that such confusion could be avoided however, by
introducing a line continuation character (or group of characters)
into R that could be used to indicate to the parser (and reader of the
code) that the expression continues onto the next line.
Something like
f - a ...
+ b ...
+ c
Cheers,
Paul
2009/3/13 Paul Suckling paul.suckl...@gmail.com:
Dear all.
After much grief I have finally found the source of some weird
discrepancies in results generated using R. It turns out that this is
due to the way R handles multi-line expressions. Here is an example
with R version 2.8.1:
# R-script...
r_parse_error - function ()
{
a - 1;
b - 1;
c - 1;
d - a + b + c;
e - a +
b +
c;
f - a
+ b
+ c;
cat('a',a,\n);
cat('b',b,\n);
cat('c',c,\n);
cat('d',d,\n);
cat('e',e,\n);
cat('f',f,\n);
}
r_parse_error();
a 1
b 1
c 1
d 3
e 3
f 1
As far as I am concerned f should have the value 3.
This is causing me endless problems since case f is our house style
for breaking up expressions for readability. All our code will need to
be rechecked as a result. Is this behaviour a bug? If not, is it
possible to get R to generate a warning that several lines of an
expression are potentially being ignored, perhaps by turning on a
strict mode which requires the semi-colons?
Thank you,
Paul
--
Nashi Power.
http://nashi.podzone.org/
Registered address: 7 Trescoe Gardens, Harrow, Middx., U.K.
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
jim holtman wrote:
if (1 == 1) {print (TRUE)
+ } else {print (FALSE)}
[1] TRUE
so the parse knows that the initial 'if' is not complete on the single line.
... and likewise the original code could be rewritten as
f - { a
+ b
+ c }
vQ
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
If all your code has semicolons you could write a program that
puts each statement on one line based on the semicolons and
then passing it through R will reformat it in a standard way.
See Rtidy.bat in the batchfiles distribution for the reformatting part:
http://batchfiles.googlecode.com
On Fri, Mar 13, 2009 at 8:55 AM, Paul Suckling paul.suckl...@gmail.com wrote:
Dear all.
After much grief I have finally found the source of some weird
discrepancies in results generated using R. It turns out that this is
due to the way R handles multi-line expressions. Here is an example
with R version 2.8.1:
# R-script...
r_parse_error - function ()
{
a - 1;
b - 1;
c - 1;
d - a + b + c;
e - a +
b +
c;
f - a
+ b
+ c;
cat('a',a,\n);
cat('b',b,\n);
cat('c',c,\n);
cat('d',d,\n);
cat('e',e,\n);
cat('f',f,\n);
}
r_parse_error();
a 1
b 1
c 1
d 3
e 3
f 1
As far as I am concerned f should have the value 3.
This is causing me endless problems since case f is our house style
for breaking up expressions for readability. All our code will need to
be rechecked as a result. Is this behaviour a bug? If not, is it
possible to get R to generate a warning that several lines of an
expression are potentially being ignored, perhaps by turning on a
strict mode which requires the semi-colons?
Thank you,
Paul
__
R-help@r-project.org mailing list
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@r-project.org mailing list
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.
Re: [R] R multiline expression grief
Gabor Grothendieck wrote:
If all your code has semicolons you could write a program that
puts each statement on one line based on the semicolons and
then passing it through R will reformat it in a standard way.
See Rtidy.bat in the batchfiles distribution for the reformatting part:
http://batchfiles.googlecode.com
for the puts each statement on one line based on the semicolons part,
it's enough to pass the program through a simple sed script, *provided*
that each line not ending in a semicolon is not a complete line:
sed -n '/;\s*$/!{H}; /;\s*$/{H;g;s/\n//g;s/;\s*$//;p;s/.//g;h}'
input output
(i guess this can be simplified.)
vQ
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
On 13-Mar-09 12:55:35, Paul Suckling wrote:
Dear all.
After much grief I have finally found the source of some weird
discrepancies in results generated using R. It turns out that this is
due to the way R handles multi-line expressions. Here is an example
with R version 2.8.1:
# R-script...
r_parse_error - function ()
{
a - 1;
b - 1;
c - 1;
d - a + b + c;
e - a +
b +
c;
f - a
+ b
+ c;
cat('a',a,\n);
cat('b',b,\n);
cat('c',c,\n);
cat('d',d,\n);
cat('e',e,\n);
cat('f',f,\n);
}
r_parse_error();
a 1
b 1
c 1
d 3
e 3
f 1
As far as I am concerned f should have the value 3.
This is causing me endless problems since case f is our house style
for breaking up expressions for readability. All our code will need to
be rechecked as a result. Is this behaviour a bug? If not, is it
possible to get R to generate a warning that several lines of an
expression are potentially being ignored, perhaps by turning on a
strict mode which requires the semi-colons?
Thank you,
Paul
The lines are not being ignored! In
e - a +
b +
c;
each line (until the last) is syntactically incomplete, so the R
parser continues on to the next line until the expression is
complete; and the ; is irrelevant for this purpose. Unlike C,
but like (say) 'awk', the ; in R serves to terminate an expression
when this is followed on the same line by another one, so it is
basically a separator.
In
f - a
+ b
+ c;
however, f - a is complete, so the value of 'a' is assigned
to f. The line + b would have sent the value of 'b' (the +
being the unary operator + which does not change anything)
to the console if it did not occur inside a function definition.
As it is, although + b is evaluated, because it is inside the
function no putput is produced. Similarly for + c; (and, once
again, the ; is irrelevant since a ; at the end of a line
does nothing -- unless the line was syntatically incomplete at
that point, in which case ; as the expression terminator
would trigger a syntax error since an incomplete expression
was being terminated. So
f - a
+ b
+ c;
is not a multiline expression. It is three expressions on three
separate lines.
The only suggestion I can make is that you have to change your
house style -- it is at odds with the way the R parser works,
and is bound to cause much grief.
Best wishes, and good luck!
Ted.
E-Mail: (Ted Harding) ted.hard...@manchester.ac.uk
Fax-to-email: +44 (0)870 094 0861
Date: 13-Mar-09 Time: 14:16:08
-- XFMail --
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
On Fri, Mar 13, 2009 at 10:11 AM, Wacek Kusnierczyk
waclaw.marcin.kusnierc...@idi.ntnu.no wrote:
Gabor Grothendieck wrote:
If all your code has semicolons you could write a program that
puts each statement on one line based on the semicolons and
then passing it through R will reformat it in a standard way.
See Rtidy.bat in the batchfiles distribution for the reformatting part:
http://batchfiles.googlecode.com
for the puts each statement on one line based on the semicolons part,
it's enough to pass the program through a simple sed script, *provided*
that each line not ending in a semicolon is not a complete line:
sed -n '/;\s*$/!{H}; /;\s*$/{H;g;s/\n//g;s/;\s*$//;p;s/.//g;h}'
input output
(i guess this can be simplified.)
One would want to be sure that a comment is not continued onto
a code line.
__
R-help@r-project.org mailing list
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.
Re: [R] R multiline expression grief
Gabor Grothendieck wrote:
On Fri, Mar 13, 2009 at 10:11 AM, Wacek Kusnierczyk
waclaw.marcin.kusnierc...@idi.ntnu.no wrote:
Gabor Grothendieck wrote:
If all your code has semicolons you could write a program that
puts each statement on one line based on the semicolons and
then passing it through R will reformat it in a standard way.
See Rtidy.bat in the batchfiles distribution for the reformatting part:
http://batchfiles.googlecode.com
for the puts each statement on one line based on the semicolons part,
it's enough to pass the program through a simple sed script, *provided*
that each line not ending in a semicolon is not a complete line:
sed -n '/;\s*$/!{H}; /;\s*$/{H;g;s/\n//g;s/;\s*$//;p;s/.//g;h}'
input output
(i guess this can be simplified.)
One would want to be sure that a comment is not continued onto
a code line.
of course; you'd have to handle comments separately.
vQ
__
R-help@r-project.org mailing list
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.
