R: Quantile-Quantile Plots

qqnorm {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, ...)
## Default S3 method:
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

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")