precrec (version 0.24.0)

classification_report: Classification report

Description

classification_report builds the per-class table of precision, recall and F-score that scikit-learn's classification_report prints, together with the summary rows that go under it.

Usage

classification_report(
  mdat,
  scores = NULL,
  labels = NULL,
  at = NULL,
  zero_division = 0,
  ...
)

Value

A data frame with one row per class and one row per summary, and the columns

modnames	Model name
dsids	Dataset ID
class	Class name, or the name of a summary row
precision	Predicted positives that are positive
recall	Positives that are predicted positive
fscore	Harmonic mean of the two
support	Observations of the class

The object also has the class classification_report, which only affects how it prints; it is a data frame in every other respect.

Arguments

mdat

An mdata object created by mmdata(). It can be omitted when scores and labels are given.

scores

A numeric vector, matrix, array, data frame, or list of scores. See mmdata() for the accepted shapes.

labels

A numeric, character, logical, or factor vector of observed labels, or a list of such vectors.

at

The operating point, as a score threshold. An observation is predicted positive for a class when its score for that class is greater than or equal to the threshold. It has no default and must be given; see the note below on why. Either

• a single number, used for every class, or

• one number per class, named after the classes or given in their order.

A score of NA is never predicted positive, matching the default na_worst = TRUE of the rest of the package.

zero_division

The value reported when a precision, recall or F-score divides by zero - a class nothing was predicted into, or a class with no observations. 0 by default, as in scikit-learn. Use NA for the convention the per-cutoff metrics of evalmod() follow.

...

Further arguments passed to mmdata() when scores and labels are given instead of mdat.

The summary rows

macro avg is the unweighted mean over the classes and weighted avg the mean weighted by support. The third row depends on whether the predictions assign each observation to exactly one class, which is the rule scikit-learn documents:

• A binary problem at a threshold predicts each observation into exactly one of the two classes, so the row is accuracy.

• A multi-class problem is evaluated by one-vs-rest, and each class is thresholded on its own, so an observation can fall into no class or into several. There is then no single-label accuracy, and the row is micro avg: precision, recall and F-score recomputed from the true positives, false positives and false negatives pooled over the classes.

Why <code>at</code> has no default

scikit-learn reports on y_pred, so the caller has already chosen an operating point before the function is called. precrec holds scores and evaluates every cutoff, so the report has to be told which one to use, and the answer changes the table: on the three-class C3N150 the F-score of one class moves from 0.37 to 0.51 between two reasonable choices. Scores in precrec are on whatever scale the classifier produced, so there is no threshold that is meaningful for all of them - 0.5 says nothing about a log-odds or an SVM margin. The threshold is therefore always the caller's.

See Also

evalmod() for the same metrics at every cutoff, auc() for the threshold-free summaries and their macro averages, and prob_metrics() for the probability-based losses.

Examples

## Multi-class: one row per class, then micro, macro and weighted averages
data(C3N150)
mdat <- mmdata(C3N150$scores, C3N150$labels)
classification_report(mdat, at = 0.5)

## A threshold per class, named or in class order
classification_report(mdat, at = c(c1 = 0.4, c2 = 0.5, c3 = 0.6))

## Binary: both classes, and an accuracy row rather than a micro average
data(P10N10)
classification_report(
  scores = P10N10$scores, labels = P10N10$labels,
  at = 12
)

## It is a data frame, so the usual accessors work
report <- classification_report(mdat, at = 0.5)
report[report$class == "macro avg", ]