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question on graphs and finding area under a curve
5 messages · Renuka Sane, Marc Schwartz, Romain Francois +2 more
On Tue, 2005-08-02 at 18:20 +0530, Renuka Sane wrote:
Question on graphs: The default case for drawing a graph in R, is where a little space is left on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) -- there will be some space between the edge of the x-axis and where 0 is placed. If I want 0 on the edge, how do I do it in R?
See ?par and take note of the 'xaxs' and 'yaxs' parameters. By default, these are set to 'r', where the axes are extended by 4% in each direction. Thus, set one or both parameters to 'i' to set the axes to exactly the ranges of xlim and/or ylim as you require.
Area under the curve: I have a 45 degree line and a curve above or below it. Is there a way in R to find the area between the two?
See Frank Harrell's somers2() function in the Hmisc package on CRAN. Among other things, it outputs a value "C", which is the AUC. HTH, Marc Schwartz
Le 02.08.2005 14:50, Renuka Sane a ??crit :
Question on graphs: The default case for drawing a graph in R, is where a little space is left on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) -- there will be some space between the edge of the x-axis and where 0 is placed. If I want 0 on the edge, how do I do it in R? Area under the curve: I have a 45 degree line and a curve above or below it. Is there a way in R to find the area between the two?
Hi, integrate.xy in sfsmisc package might help you. Romain
Thanks, Renuka
- visit the R Graph Gallery : http://addictedtor.free.fr/graphiques ~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~ ~~~~~~ Romain FRANCOIS - http://addictedtor.free.fr ~~~~~~ ~~~~ Etudiant ISUP - CS3 - Industrie et Services ~~~~ ~~ http://www.isup.cicrp.jussieu.fr/ ~~ ~~~~ Stagiaire INRIA Futurs - Equipe SELECT ~~~~ ~~~~~~ http://www.inria.fr/recherche/equipes/select.fr.html ~~~~~~ ~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~
Hi,
To find the area lying between the curve y = y(x) and 45 degree line (which,
assuming it goes through the origin, is y = x), you can use the following
function based on trapezoidal rule:
trap.rule <- function(x,f) {sum(diff(x)*(f[-1]+f[-length(f)]))/2}
trap.rule(x,f=y-x)
This area will be negative if y(x) is below the 45 degree line.
However, your question is not complete, I think. You need to specify the
interval of integration. For this you may need to determine the points of
intersection of the two curves, which involves the solution of a fixed point
problem.
Hope this helps,
Ravi.
-----Original Message----- From: r-help-bounces at stat.math.ethz.ch [mailto:r-help- bounces at stat.math.ethz.ch] On Behalf Of Renuka Sane Sent: Tuesday, August 02, 2005 8:51 AM To: r-help at stat.math.ethz.ch Subject: [R] question on graphs and finding area under a curve Question on graphs: The default case for drawing a graph in R, is where a little space is left on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) - - there will be some space between the edge of the x-axis and where 0 is placed. If I want 0 on the edge, how do I do it in R? Area under the curve: I have a 45 degree line and a curve above or below it. Is there a way in R to find the area between the two? Thanks, Renuka -- Renuka Sane http://www.nyx.net/~rsane [[alternative HTML version deleted]]
______________________________________________ R-help at stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting- guide.html
Also see function rocdemo.sca in the ROC package. The area under the 45 degree line in an ROC curve has an area of 0.5. Regards, Adai
On Tue, 2005-08-02 at 09:24 -0400, Ravi Varadhan wrote:
Hi,
To find the area lying between the curve y = y(x) and 45 degree line (which,
assuming it goes through the origin, is y = x), you can use the following
function based on trapezoidal rule:
trap.rule <- function(x,f) {sum(diff(x)*(f[-1]+f[-length(f)]))/2}
trap.rule(x,f=y-x)
This area will be negative if y(x) is below the 45 degree line.
However, your question is not complete, I think. You need to specify the
interval of integration. For this you may need to determine the points of
intersection of the two curves, which involves the solution of a fixed point
problem.
Hope this helps,
Ravi.
-----Original Message----- From: r-help-bounces at stat.math.ethz.ch [mailto:r-help- bounces at stat.math.ethz.ch] On Behalf Of Renuka Sane Sent: Tuesday, August 02, 2005 8:51 AM To: r-help at stat.math.ethz.ch Subject: [R] question on graphs and finding area under a curve Question on graphs: The default case for drawing a graph in R, is where a little space is left on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) - - there will be some space between the edge of the x-axis and where 0 is placed. If I want 0 on the edge, how do I do it in R? Area under the curve: I have a 45 degree line and a curve above or below it. Is there a way in R to find the area between the two? Thanks, Renuka -- Renuka Sane http://www.nyx.net/~rsane [[alternative HTML version deleted]]
______________________________________________ R-help at stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting- guide.html
______________________________________________ R-help at stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html