performanceObject to capture the result of a performance evaluation, optionally collecting evaluations from several cross-validation or bootstrapping runs.
x.namePerformance measure used for the x axis.
y.namePerformance measure used for the y axis.
alpha.nameName of the unit that is used to create the parametrized
curve. Currently, curves can only be parametrized by cutoff, so
alpha.name is either none or cutoff.
x.valuesA list in which each entry contains the x values of the curve
of this particular cross-validation run. x.values[[i]],
y.values[[i]], and alpha.values[[i]] correspond to each
other.
y.valuesA list in which each entry contains the y values of the curve of this particular cross-validation run.
alpha.valuesA list in which each entry contains the cutoff values of the curve of this particular cross-validation run.
Objects can be created by using the performance function.
A performance object can capture information from four
different evaluation scenarios:
The behaviour of a cutoff-dependent performance measure across
the range of all cutoffs (e.g. performance( predObj, 'acc' ) ). Here,
x.values contains the cutoffs, y.values the
corresponding values of the performance measure, and
alpha.values is empty.
The trade-off between two performance measures across the
range of all cutoffs (e.g. performance( predObj,
'tpr', 'fpr' ) ). In this case, the cutoffs are stored in
alpha.values, while x.values and y.values
contain the corresponding values of the two performance measures.
A performance measure that comes along with an obligatory
second axis (e.g. performance( predObj, 'ecost' ) ). Here, the measure values are
stored in y.values, while the corresponding values of the
obligatory axis are stored in x.values, and alpha.values
is empty.
A performance measure whose value is just a scalar
(e.g. performance( predObj, 'auc' ) ). The value is then stored in
y.values, while x.values and alpha.values are
empty.
A detailed list of references can be found on the ROCR homepage at http://rocr.bioinf.mpi-sb.mpg.de.