Displays a cumulative normal percentage probability (CPP) plot, equivalent to a Q-Q plot, as has been traditionally used by physical scientists and engineers.
cnpplt(xx, xlab = deparse(substitute(xx)),
ylab = "% Cumulative Probability", log = FALSE, xlim = NULL,
main = "", ifqs = FALSE, ifshape = FALSE, pch = 3,
cex = 0.8, cexp = 1, cex.axis = 0.8, ...)
name of the variable to be plotted.
by default the character string for xx
is used for the x-axis title. An alternate title can be displayed with xlab = "text string"
, see Examples.
a title for the y-axis, defaults to "% Cumulative Probability".
to display the data with logarithmic (x-axis) scaling, set log = TRUE
.
when used stand-alone a title may be added optionally above the plot by setting main
, e.g., main = "Kola Ecogeochemistry Project, 1995"
.
setting ifqs = TRUE
results in horizontal and vertical dotted lines being plotted at the three central quartiles and their values, respectively.
by default the plotting symbol is set to a plus, pch = 3
, alternate plotting symbols may be chosen from those displayed by display.marks
, see also Note below.
by default the size of the text for data set size, N, is set to 80%, i.e. cex = 0.8
, and may be changed if required.
by default the size of the plotting symbol, pch
, is set to 100%, and may be changed if required.
if overplotting occurs in the y-axis labelling the size of the y-axis labels may be reduced by setting cex.axis
to a number smaller than the default of cex.axis = 0.8
.
further arguments to be passed to methods. For example, the size of the axis titles by setting cex.lab
, and the size of the plot title by setting cex.main
. For example, if it is required to make the plot title smaller, add cex.main = 0.9
to reduce the font size by 10%. The colour of the plotting symbols may be changed from the default black, e.e., col = 2
for red.
If the default selection for xlim
is inappropriate it can be set, e.g., xlim = c(0, 200)
or c(2, 200)
, the latter being appropriate for a logarithmically scaled plot, i.e. log = TRUE
. If the defined limits lie within the observed data range a truncated plot will be displayed. If this occurs the number of data points omitted is displayed below the total number of observations.
If it is desired to prepare a display of data falling within a defined part of the actual data range, then either a data subset can be prepared externally using the appropriate R syntax, or xx
may be defined in the function call as, for example, Cu[Cu < some.value]
which would remove the influence of one or more outliers having values greater than some.value
. In this case the number of data values displayed will be the number that are <some.value
.
# NOT RUN {
## Make test data available
data(kola.o)
attach(kola.o)
## A stand-alone cumulative normal percentage probability plot
cnpplt(Cu)
## A more appropriately labelled and scaled cumulative normal percentage
## probability plot using a cross/x rather than a plus
cnpplt(Cu, xlab = "Cu (mg/kg) in <2 mm O-horizon soil", log = TRUE,
pch = 4)
## Detach test data
detach(kola.o)
# }
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