| % File src/library/stats/man/qqnorm.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2012 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{qqnorm} |
| \title{Quantile-Quantile Plots} |
| \usage{ |
| qqnorm(y, \dots) |
| \method{qqnorm}{default}(y, ylim, main = "Normal Q-Q Plot", |
| xlab = "Theoretical Quantiles", ylab = "Sample Quantiles", |
| plot.it = TRUE, datax = FALSE, \dots) |
| |
| qqline(y, datax = FALSE, distribution = qnorm, |
| probs = c(0.25, 0.75), qtype = 7, \dots) |
| |
| qqplot(x, y, plot.it = TRUE, xlab = deparse(substitute(x)), |
| ylab = deparse(substitute(y)), \dots) |
| } |
| \alias{qqnorm} |
| \alias{qqnorm.default} |
| \alias{qqplot} |
| \alias{qqline} |
| \concept{normal probability plot} % PR#12095 |
| |
| \arguments{ |
| \item{x}{The first sample for \code{qqplot}.} |
| \item{y}{The second or only data sample.} |
| \item{xlab, ylab, main}{plot labels. The \code{xlab} and \code{ylab} |
| refer to the y and x axes respectively if \code{datax = TRUE}.} |
| \item{plot.it}{logical. Should the result be plotted?} |
| \item{datax}{logical. Should data values be on the x-axis?} |
| \item{distribution}{quantile function for reference theoretical distribution.} |
| \item{probs}{numeric vector of length two, representing probabilities. |
| Corresponding quantile pairs define the line drawn.} |
| \item{qtype}{the \code{type} of quantile computation used in \code{\link{quantile}}.} |
| |
| \item{ylim, \dots}{graphical parameters.} |
| } |
| \description{ |
| \code{qqnorm} is a generic function the default method of which |
| produces a normal QQ plot of the values in \code{y}. |
| \code{qqline} adds a line to a \dQuote{theoretical}, by default |
| normal, quantile-quantile plot which passes through the \code{probs} |
| quantiles, by default the first and third quartiles. |
| |
| \code{qqplot} produces a QQ plot of two datasets. |
| |
| Graphical parameters may be given as arguments to \code{qqnorm}, |
| \code{qqplot} and \code{qqline}. |
| } |
| \value{ |
| For \code{qqnorm} and \code{qqplot}, a list with components |
| \item{x}{The x coordinates of the points that were/would be plotted} |
| \item{y}{The original \code{y} vector, i.e., the corresponding y |
| coordinates \emph{including \code{\link{NA}}s}.} |
| } |
| \references{ |
| Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) |
| \emph{The New S Language}. |
| Wadsworth & Brooks/Cole. |
| } |
| \seealso{ |
| \code{\link{ppoints}}, used by \code{qqnorm} to generate |
| approximations to expected order statistics for a normal distribution. |
| } |
| \examples{ |
| require(graphics) |
| |
| y <- rt(200, df = 5) |
| qqnorm(y); qqline(y, col = 2) |
| qqplot(y, rt(300, df = 5)) |
| |
| qqnorm(precip, ylab = "Precipitation [in/yr] for 70 US cities") |
| |
| ## "QQ-Chisquare" : -------------------------- |
| y <- rchisq(500, df = 3) |
| ## Q-Q plot for Chi^2 data against true theoretical distribution: |
| qqplot(qchisq(ppoints(500), df = 3), y, |
| main = expression("Q-Q plot for" ~~ {chi^2}[nu == 3])) |
| qqline(y, distribution = function(p) qchisq(p, df = 3), |
| probs = c(0.1, 0.6), col = 2) |
| mtext("qqline(*, dist = qchisq(., df=3), prob = c(0.1, 0.6))") |
| ## (Note that the above uses ppoints() with a = 1/2, giving the |
| ## probability points for quantile type 5: so theoretically, using |
| ## qqline(qtype = 5) might be preferable.) |
| } |
| \keyword{hplot} |
| \keyword{distribution} |