qqnorm                 package:base                 R Documentation

Quantile-Quantile Plots

Description:

     `qqnorm' is a generic functions the default method of which
     produces a normal QQ plot of the values in `y'. `qqline' adds a
     line to a normal quantile-quantile plot which passes through the
     first and third quartiles.

     `qqplot' produces a QQ plot of two datasets.

     Graphical parameters may be given as arguments to `qqnorm',
     `qqplot' and `qqline'.

Usage:

     qqnorm(y, ...)
     qqnorm(y, ylim, main = "Normal Q-Q Plot",
            xlab = "Theoretical Quantiles",
            ylab = "Sample Quantiles", plot.it = TRUE, ...)
     qqline(y, ...)
     qqplot(x, y, plot.it = TRUE, xlab = deparse(substitute(x)),
            ylab = deparse(substitute(y)), ...)

Arguments:

       x: The first sample for `qqplot'.

       y: The second or only data sample.

xlab, ylab, main: plot labels.

 plot.it: logical. Should the result be plotted?

ylim, ...: graphical parameters.

Value:

     For `qqnorm' and `qqplot', a list with components 

       x: The x coordinates of the points that were/would be plotted

       y: The corresponding y coordinates

See Also:

     `ppoints'.

Examples:

     y <- rt(200, df = 5)
     qqnorm(y); qqline(y, col = 2)
     qqplot(y, rt(300, df = 5))
     data(precip)
     qqnorm(precip, ylab = "Precipitation [in/yr] for 70 US cities")

