qqnorm

From stats v3.2.2 by R-core R-core@R-project.org

Quantile-Quantile Plots

qqnorm is a generic function the default method of which produces a normal QQ plot of the values in y. qqline adds a line to a “theoretical”, by default normal, quantile-quantile plot which passes through the probs quantiles, by default 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.

Keywords: hplot, distribution

Usage

qqnorm(y, ...)
"qqnorm"(y, ylim, main = "Normal Q-Q Plot", xlab = "Theoretical Quantiles", ylab = "Sample Quantiles", plot.it = TRUE, datax = FALSE, ...)
qqline(y, datax = FALSE, distribution = qnorm, probs = c(0.25, 0.75), qtype = 7, ...)
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. The xlab and ylab refer to the y and x axes respectively if datax = TRUE.
plot.it: logical. Should the result be plotted?
datax: logical. Should data values be on the x-axis?
distribution: quantile function for reference theoretical distribution.
probs: numeric vector of length two, representing probabilities. Corresponding quantile pairs define the line drawn.
qtype: the type of quantile computation used in quantile.
ylim, ...: graphical parameters.

Value

x: The x coordinates of the points that were/would be plotted
y: The original y vector, i.e., the corresponding y coordinates including NAs.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Examples

library(stats)

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),
       prob = c(0.1, 0.6), col = 2)
mtext("qqline(*, dist = qchisq(., df=3), prob = c(0.1, 0.6))")

Documentation reproduced from package stats, version 3.2.2, License: Part of R 3.2.2

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