Jason, All these are clearly defined in the help file for 'boxplot' under 'range'. Don't understand how you missed that.
...Tao ----- Original Message ---- > From: Jason Rupert <jasonkrup...@yahoo.com> > To: Dennis Murphy <djmu...@gmail.com> > Cc: R Project Help <R-help@r-project.org> > Sent: Wed, May 12, 2010 3:40:12 AM > Subject: Re: [R] Whiskers on the default boxplot {graphics} > > Fantastic! It would be great if the description could be modified to > include the mysterious bit about the upper and lower bound whisker > positions: upper whisker = min(max(x), Q_3 + 1.5 * IQR) lower whisker > = max(min(x), Q_1 - 1.5 * IQR) Maybe that is clearly written in the > description of boxplot.stats {grDevices}, but evidently I missed it numerous > times and also did not pick up on this intent from the original description > of > boxplot {graphics}. Your type of descriptive answer and > helpfulness is much appreciated and one of the reasons I continue to endorse > the > R tool over numerous others. More like you and the tool may be > headed for domination in the market. Thanks > again! ________________________________ From: > Dennis Murphy < > href="mailto:djmu...@gmail.com">djmu...@gmail.com> Cc: R Project > Help < > href="mailto:R-help@r-project.org">R-help@r-project.org> Sent: Wed, > May 12, 2010 2:50:19 AM Subject: Re: [R] Whiskers on the default boxplot > {graphics} Hi: Let's do some math > :) e: Okay...Let me see if I've got > it... > >>I'm just trying to use the default boxplot {graphics} > capability in R... > >>So I call something like the > following: >>> boxplot(mpg~cyl,data=mtcars, main="Car Milage Data", > xlab="Number of Cylinders", ylab="Miles Per Gallon") \ > >>That > produces something as shown in the > following: >http://www.statmethods.net/graphs/images/boxplot1.jpg > >>When > that default boxplot is called, i.e. boxplot {graphics}, as shown in the line > of > code above, it is actually calling into boxplot.stats {grDevices}. When > boxplot.stats {grDevices} is called it has a default value for "coef" of 1.5, > i.e. coef = 1.5. > >>If I understand the purpose of "coef" > correctly, it means that the ‘whiskers’ should extend out 1.5 times the > length > of the box away from the box. Is that correct? > If by > 'length of the box' you mean the interquartile range (IQR = Q_3 - Q_1 where Q > refers to quartile), then assuming that x is the numeric vector of interest > for a boxplot, upper whisker = min(max(x), Q_3 + 1.5 * IQR) lower > whisker = max(min(x), Q_1 - 1.5 * IQR) So the upper whisker is located at > the *smaller* of the maximum x value and Q_3 + 1.5 IQR, whereas the lower > whisker is located at the *larger* of the smallest x value and Q_1 - 1.5 > IQR. In your terms, the whiskers should extend out a *maximum* of "1.5 > times the length of the box away from the box". Visually, this means > that individual points more extreme in value than Q3 + 1.5 IQR are > plotted separately at the high end, and those below Q1 - 1.5 IQR are plotted > separately on the low end. Depending on the source, the separately plotted > points are called 'outside values'. On the other hand, if the maximum or > minimum values of x are closer than 1.5 IQR in distance from its nearest > quartile, then that is where the whisker is positioned. Does that make > sense? HTH, Dennis >>Now I look back at the plot, and > I'm not sure how 1.5 times the length of the box corresponds with the whisker > lengths shown in the image: > > href="http://www.statmethods.net/graphs/images/boxplot1.jpg" target=_blank > >http://www.statmethods.net/graphs/images/boxplot1.jpg > >>Is > it that the whisker length is a total of 1.5 the length of the box and > centered > about the median (2nd Quartile)? > >>Just trying to get a handle > on this, so thanks again for all the help in deciphering > this. > > > > > > > >>________________________________ >>From: > RJ Cunningham < > href="mailto:ro...@iinet.net.au">ro...@iinet.net.au> > > > target="_blank" href="http://ast.net">ast.net> >>Cc: R Project > Help < > href="mailto:R-help@r-project.org">R-help@r-project.org> >>Sent: > Tue, May 11, 2010 9:57:48 PM > >Subject: Re: [R] Whiskers on the > default boxplot {graphics} > > >I think not. Isn't the > "secret" here? > > >>Arguments: > >>x: a > numeric vector for which the boxplot will be constructed >>('NA's and > 'NaN's are allowed and omitted). > >>coef: this determines how > far the plot 'whiskers' extend out >>from the box. If 'coef' is > positive, the whiskers extend >>to the most extreme data point which is > no more than >>'coef' times the length of the box away from the box. > A >>value of zero causes the whiskers to extend to the > data >>extremes (and no outliers be > returned). > >>do.conf,do.out: logicals; if 'FALSE', the 'conf' > or 'out' >>component respectively will be empty in the > result. > >>Details: > >>The two 'hinges' are > versions of the first and third quartile,... > > >>On Wed > May 12 10:35 , Jason Rupert sent: > > >>Humm....Maybe > I need to look some place else than boxplot.stats {grDevices} for a > definition > of how the upper/lower whiskers are > produced. >>> >>>> >>>By any chance are > they "the lowest datum still within 1.5 IQR of the lower quartile, and the > highest datum still within 1.5 IQR of the upper > quartile"? >>> >>>> >>>None of the links > from boxplot.stats {grDevices} seemed to reveal the secret definition of the > R > whiskers. >>> >>>> >>>Thanks > again. >>> >>> >>> >>> >>> >>>> >>>----- > Original Message > ---- >>>> > >>>> > >>To: > David Winsemius < > href="mailto:dwinsem...@comcast.net">dwinsem...@comcast.net> >>>> >>>Cc: > R Project Help < > href="mailto:R-help@r-project.org">R-help@r-project.org> >>>> >>>Sent: > Tue, May 11, 2010 9:26:25 PM >>>> >>>Subject: Re: [R] > Whiskers on the default boxplot > {graphics} >>> >>>> >>>Wowzers... >>> >>>> >>>From > ?boxplot.stats: >>> >>>> >>>Details >>> >>>> >>The > two ‘hinges’ are versions of the first and third quartile, i.e., close to > quantile(x, c(1,3)/4). The hinges equal the quartiles for odd n (where n <- > length(x)) and differ for even n. Whereas the quartiles only equal > observations > for n %% 4 == 1 (n = 1 mod 4), the hinges do so additionally for n %% 4 == 2 > (n > = 2 mod 4), and are in the middle of two observations > otherwise. > >> >>>> >>>The notches > (if requested) extend to +/-1.58 IQR/sqrt(n). This seems to be based on the > same > calculations as the formula with 1.57 in Chambers et al. (1983, p. 62), given > in > McGill et al. (1978, p. 16). They are based on asymptotic normality of the > median and roughly equal sample sizes for the two medians being compared, and > are said to be rather insensitive to the underlying distributions of the > samples. The idea appears to be to give roughly a 95% confidence interval for > the difference in two > medians. >> >> >>> >>> >>>> >>>Is > a notch equal to the upper/lower whisker? Is this just a difference of > terminology or > something? >>> >>>> >>>Thanks again for > all the > insights. >>> >>> >>> >>> >>>> >>>----- > Original Message ---- >>>> > >>From: David > Winsemius < > href="mailto:dwinsem...@comcast.net">dwinsem...@comcast.net> >>>> > >>>> >>>Cc: > R Project Help < > href="mailto:R-help@r-project.org">R-help@r-project.org> >>>> >>>Sent: > Tue, May 11, 2010 9:00:15 PM >>>> >>>Subject: Re: [R] > Whiskers on the default boxplot > {graphics} >>> >>> >>>> >>>On > May 11, 2010, at 9:45 PM, Jason Rupert > wrote: >>> >>>> >>>> How are the > lower/upper whiskers defined in the default version of boxplot > {graphics}? >>>> >>>> >>>> >>> > I tried help(boxplot) and searching > href="http://www.rseek.org">www.rseek.org, but I was unable to determine an > absolute answer. > >> >>>> >>>You need > to follow the links from the help pages and tin this case it appears that you > did not follow the one > to >>> >>>> >>>?boxplot.stats >>> >>>> >>>> >>>> >>> > I checked out the definition of boxplot according to Wikipedia > (http://en.wikipedia.org/wiki/Box_plot%5C), but it also had several > approaches > >>> >>>> listed for how the > whiskers could be determined, so I'm just curious how the > default >>>> >>>> boxplot {graphics} does > it. >>>> >>>> >>>> >>>> > Thanks for any > feedback >>> >>>> >>>Follow links with > the R help system. >>> >>>> >>>> and > insights. >>> >>> >>> >>>> >>>David > Winsemius, MD >>>> >>>West Hartford, > CT >>> >>> >>> >>> >>>> >>>______________________________________________ > >> > ymailto="mailto:R-help@r-project.org" > href="mailto:R-help@r-project.org">R-help@r-project.org mailing > list >>> > target=_blank > >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. >>> >>> >>> >>> >>> >>>> >>>______________________________________________ >>> > ymailto="mailto:R-help@r-project.org" > href="mailto:R-help@r-project.org">R-help@r-project.org mailing > list >>> > target=_blank > >https://stat.ethz.ch/mailman/listinfo/r-help >>>> >>>PLEASE > do read the posting guide > target=_blank > >http://www.R-project.org/posting-guide.html >>>> >>>and > provide commented, minimal, self-contained, reproducible > code. >>> > > > > > > [[alternative HTML version > deleted]] > > >______________________________________________ > > ymailto="mailto:R-help@r-project.org" > href="mailto:R-help@r-project.org">R-help@r-project.org mailing > list > > >https://stat.ethz.ch/mailman/listinfo/r-help >>PLEASE do read the > posting guide > target=_blank >http://www.R-project.org/posting-guide.html >>and > provide commented, minimal, self-contained, reproducible > code. > > > [[alternative HTML version deleted]] ______________________________________________ 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.