i am having some problems with a program that i am writing and i think that
knowing how the while command works will help me to figure out where i am
going wrong
*when do you get kicked out of a while loop?*
(i.e., in the following example what would the final value of 'a' be?)
i
thought it would be 99 but running it in R i get 101 (and 101 for x too!)
while (x <100) {
for (i in 1:101) {
i -> x
x -> a
}
}
while this is a crude example, it is the basic form of what i am trying to
do, and i am guessing that while is not what i am looking for...
jimi adams
Department of Sociology
The Ohio State University
300 Bricker Hall
190 N Oval Mall
Columbus, OH 43210-1353
614-688-4261
our mind has a remarkable ability to think of contents as being independent
of the act of thinking
-georg simmel
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The for loop is nested inside the while loop, so it is finished before the next iteration of the while loop is attempted. So, in short, the for loop ran 101 times, ending with i, x, and a all equal to 101. Then the condition of the while loop is checked, (and not satisfied). Andy> -----Original Message----- > From: jimi adams [mailto:imij at columbus.rr.com] > Sent: Wednesday, March 20, 2002 2:39 PM > To: r-help at stat.math.ethz.ch > Subject: [R] how does while work > > > i am having some problems with a program that i am writing > and i think that > knowing how the while command works will help me to figure > out where i am > going wrong > *when do you get kicked out of a while loop?* > (i.e., in the following example what would the final value > of 'a' be?) i > thought it would be 99 but running it in R i get 101 (and 101 > for x too!) > > while (x <100) { > for (i in 1:101) { > i -> x > x -> a > } > } > > while this is a crude example, it is the basic form of what i > am trying to > do, and i am guessing that while is not what i am looking for... > > jimi adams > Department of Sociology > The Ohio State University > 300 Bricker Hall > 190 N Oval Mall > Columbus, OH 43210-1353 > 614-688-4261 > > our mind has a remarkable ability to think of contents as > being independent > of the act of thinking > -georg simmel >> -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. > -.-.-.-.-.-.-.-.- > r-help mailing list -- Read > http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html > Send "info", "help", or "[un]subscribe" > (in the "body", not the subject !) To: > r-help-request at stat.math.ethz.ch > _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._. > _._._._._._._._._ >-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
assuming you enter the while loop with a value of x less than 100, the for loop sets, in its last iteration, a=x=101 (which is the last value `i' takes). at this point you also exit the while loop, since x<100 is false. Giovanni> From: "jimi adams" <imij at columbus.rr.com> > Date: Wed, 20 Mar 2002 14:39:13 -0500 > X-Priority: 3 > X-MSMail-Priority: Normal > X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 > Sender: owner-r-help at stat.math.ethz.ch > Precedence: SfS-bulk > Content-Type: text/plain; > charset="iso-8859-1" > Content-Length: 1205 > > i am having some problems with a program that i am writing and i think that > knowing how the while command works will help me to figure out where i am > going wrong > *when do you get kicked out of a while loop?* > (i.e., in the following example what would the final value of 'a' be?) i > thought it would be 99 but running it in R i get 101 (and 101 for x too!) > > while (x <100) { > for (i in 1:101) { > i -> x > x -> a > } > } > > while this is a crude example, it is the basic form of what i am trying to > do, and i am guessing that while is not what i am looking for... > > jimi adams > Department of Sociology > The Ohio State University > 300 Bricker Hall > 190 N Oval Mall > Columbus, OH 43210-1353 > 614-688-4261 > > our mind has a remarkable ability to think of contents as being independent > of the act of thinking > -georg simmel > > > -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- > r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html > Send "info", "help", or "[un]subscribe" > (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch > _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._ >-- __________________________________________________ [ ] [ Giovanni Petris GPetris at uark.edu ] [ Department of Mathematical Sciences ] [ University of Arkansas - Fayetteville, AR 72701 ] [ Ph: (479) 575-6324, 575-8630 (fax) ] [ http://definetti.uark.edu/~gpetris/ ] [__________________________________________________] -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
On Wed, 20 Mar 2002, jimi adams wrote:> i am having some problems with a program that i am writing and i think that > knowing how the while command works will help me to figure out where i am > going wrong > *when do you get kicked out of a while loop?* > (i.e., in the following example what would the final value of 'a' be?) i > thought it would be 99 but running it in R i get 101 (and 101 for x too!) > > while (x <100) { > for (i in 1:101) { > i -> x > x -> a > } > }If you are trying to jump out of a for loop early then try something like: for (i in 1:101) { i -> x if (! x<100 ) { break } x -> a } the "next" command will also skip the rest of the body of the loop and start on the next iteration. Hope this helps, -- Greg Snow, PhD Office: 223A TMCB Department of Statistics Phone: (801) 378-7049 Brigham Young University Dept.: (801) 378-4505 Provo, UT 84602 email: gls at byu.edu -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
On Wed, 20 Mar 2002, jimi adams wrote:> i am having some problems with a program that i am writing and i think that > knowing how the while command works will help me to figure out where i am > going wrong > *when do you get kicked out of a while loop?* > (i.e., in the following example what would the final value of 'a' be?) i > thought it would be 99 but running it in R i get 101 (and 101 for x too!) > > while (x <100) { > for (i in 1:101) { > i -> x > x -> a > } > *here* > }Essentially the while condition doesn't get checked until just before the last curly brace (where I inserted *here* above), so the for loop gets to do it's thing until i (and x and a) reach 101 and only then is the while condition allowed to drop you out of the loop.> while this is a crude example, it is the basic form of what i am trying to > do, and i am guessing that while is not what i am looking for...what exactly are you trying to do? daver +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |David Richmond It works on a | + Dept. of Sociology complex scientific + |Saint Mary's College principle, known as | + Notre Dame, IN 46556 "pot luck." + |574-284-4517 - The Doctor | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
What he wanted is a mechanism to "watch" for a condition on a variable, and stop execution as soon as that condition is TRUE, regardless of where in the program. The only thing that I know of that sort of does this is inside gdb, the GNU debugger. AFAIK this is impossible. If anyone has better idea, I'd like to hear about it, too. Andy> -----Original Message----- > From: David A Richmond [mailto:richmond at saintmarys.edu] > Sent: Thursday, March 21, 2002 11:00 AM > To: jimi adams > Cc: r-help at stat.math.ethz.ch > Subject: Re: [R] how does while work > > > On Wed, 20 Mar 2002, jimi adams wrote: > > > i am having some problems with a program that i am writing > and i think that > > knowing how the while command works will help me to figure > out where i am > > going wrong > > *when do you get kicked out of a while loop?* > > (i.e., in the following example what would the final value > of 'a' be?) i > > thought it would be 99 but running it in R i get 101 (and > 101 for x too!) > > > > while (x <100) { > > for (i in 1:101) { > > i -> x > > x -> a > > } > > *here* > > } > > Essentially the while condition doesn't get checked until > just before the > last curly brace (where I inserted *here* above), so the for > loop gets to > do it's thing until i (and x and a) reach 101 and only then > is the while > condition allowed to drop you out of the loop. > > > while this is a crude example, it is the basic form of what > i am trying to > > do, and i am guessing that while is not what i am looking for... > > what exactly are you trying to do? > > daver > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > |David Richmond It works on a | > + Dept. of Sociology complex scientific + > |Saint Mary's College principle, known as | > + Notre Dame, IN 46556 "pot luck." + > |574-284-4517 - The Doctor | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. > -.-.-.-.-.-.-.-.- > r-help mailing list -- Readhttp://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._. _._ -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
Don't think so. stop() and warning() will only be triggered when explicited
told to do so. Thus, essentially the (only?) idiotic way to do it is insert
if(x>=100) stop("x>100!") everywhere. There's no mechanism
to keep track of
a variable as the program executes, AFAIK.
Andy
> -----Original Message-----
> From: Giovanni Petris [mailto:GPetris at uark.edu]
> Sent: Thursday, March 21, 2002 3:17 PM
> To: andy_liaw at merck.com
> Cc: richmond at saintmarys.edu; imij at columbus.rr.com;
> r-help at stat.math.ethz.ch
> Subject: Re: [R] how does while work
>
>
>
> Maybe warning() or stop() can be used for this purpose.
>
> Giovanni
>
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> > Date: Thu, 21 Mar 2002 12:55:15 -0500
> > From: "Liaw, Andy" <andy_liaw at merck.com>
> > cc: r-help at stat.math.ethz.ch
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> >
> > What he wanted is a mechanism to "watch" for a condition on
> a variable, and
> > stop execution as soon as that condition is TRUE,
> regardless of where in the
> > program. The only thing that I know of that sort of does
> this is inside
> > gdb, the GNU debugger. AFAIK this is impossible. If
> anyone has better
> > idea, I'd like to hear about it, too.
> >
> > Andy
> >
> > > -----Original Message-----
> > > From: David A Richmond [mailto:richmond at saintmarys.edu]
> > > Sent: Thursday, March 21, 2002 11:00 AM
> > > To: jimi adams
> > > Cc: r-help at stat.math.ethz.ch
> > > Subject: Re: [R] how does while work
> > >
> > >
> > > On Wed, 20 Mar 2002, jimi adams wrote:
> > >
> > > > i am having some problems with a program that i am writing
> > > and i think that
> > > > knowing how the while command works will help me to figure
> > > out where i am
> > > > going wrong
> > > > *when do you get kicked out of a while loop?*
> > > > (i.e., in the following example what would the final value
> > > of 'a' be?) i
> > > > thought it would be 99 but running it in R i get 101 (and
> > > 101 for x too!)
> > > >
> > > > while (x <100) {
> > > > for (i in 1:101) {
> > > > i -> x
> > > > x -> a
> > > > }
> > > > *here*
> > > > }
> > >
> > > Essentially the while condition doesn't get checked until
> > > just before the
> > > last curly brace (where I inserted *here* above), so the for
> > > loop gets to
> > > do it's thing until i (and x and a) reach 101 and only then
> > > is the while
> > > condition allowed to drop you out of the loop.
> > >
> > > > while this is a crude example, it is the basic form of what
> > > i am trying to
> > > > do, and i am guessing that while is not what i am looking
for...
> > >
> > > what exactly are you trying to do?
> > >
> > > daver
> > >
> > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > > |David Richmond It works on a |
> > > + Dept. of Sociology complex scientific +
> > > |Saint Mary's College principle, known as |
> > > + Notre Dame, IN 46556 "pot luck." +
> > > |574-284-4517 - The Doctor |
> > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > >
> > > -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
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>
> --
>
> __________________________________________________
> [ ]
> [ Giovanni Petris GPetris at uark.edu ]
> [ Department of Mathematical Sciences ]
> [ University of Arkansas - Fayetteville, AR 72701 ]
> [ Ph: (479) 575-6324, 575-8630 (fax) ]
> [ http://definetti.uark.edu/~gpetris/ ]
> [__________________________________________________]
>
>
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This thread is fast becoming a citation classic. I thought it would have
been resolved in a one-liner, but...
What you really want to know is how Boolean logic works in stack-based
computing. while() and for() evaluate their conditional(s) before
executing the statement(s) that they are controlling. do() evaluates
after execution. However, they all depend upon the same operator to
delimit the statement(s) that they control (in R at least). Thus, you
aren't allowed to do what jimi wants, to evaluate the while() condition
before the for() condition like this:
while (x <100) {
for (i in 1:101) {
i -> x
x -> a
} # end of while()
} # end of for()
What has to be done is something like this:
for(i in 1:101) {
x<-i
if(x<100) a<-x
}
Now the conditional (x<100) takes precedence over the assignment, which
was what was intended. Before anyone accuses me of preaching, I have
made the same mistake (and worse) many times.
Jim
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