Iterative Partitioning Filter

Description

Ensemble-based filter for removing label noise from a dataset as a preprocessing step of classification. For more information, see 'Details' and 'References' sections.

Usage

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## S3 method for class 'formula'
IPF(formula, data, ...)

## Default S3 method:
IPF(x, nfolds = 5, consensus = FALSE, p = 0.01, s = 3,
  y = 0.5, classColumn = ncol(x), ...)

Arguments

formula

A formula describing the classification variable and the attributes to be used.

data, x

Data frame containing the tranining dataset to be filtered.

...

Optional parameters to be passed to other methods.

nfolds

Number of partitions in each iteration.

consensus

Logical. If FALSE, majority voting scheme is used. If TRUE, consensus voting scheme is applied.

p

Real number between 0 and 1. It sets the minimum proportion of original instances which must be tagged as noisy in order to go for another iteration.

s

Positive integer setting the stop criterion together with p. The filter stops after s iterations with not enough noisy instances removed (according to the proportion p, see the 'Details' ).

y

Real number between 0 and 1. It sets the proportion of good instances which must be stored in each iteration.

classColumn

Positive integer indicating the column which contains the (factor of) classes. By default, the last column is considered.

Details

The full description of the method can be looked up in the provided references. A base classifier is built in each of the nfolds partitions of data. Then, they are tested in the whole dataset, and the removal of noisy instances is decided via consensus or majority voting schemes. Finally, a proportion of good instances (i.e. those whose label agrees with all the base classifiers) is stored and removed for the next iteration. The process stops after s iterations with not enough (according to the proportion p) noisy instances removed. In this implementation, the base classifier used is C4.5.

Value

An object of class filter, which is a list with seven components:

  • cleanData is a data frame containing the filtered dataset.

  • remIdx is a vector of integers indicating the indexes for removed instances (i.e. their row number with respect to the original data frame).

  • repIdx is a vector of integers indicating the indexes for repaired/relabelled instances (i.e. their row number with respect to the original data frame).

  • repLab is a factor containing the new labels for repaired instances.

  • parameters is a list containing the argument values.

  • call contains the original call to the filter.

  • extraInf is a character that includes additional interesting information not covered by previous items.

Note

By means of a message, the number of noisy instances removed in each iteration is displayed in the console.

References

Khoshgoftaar T. M., Rebours P. (2007): Improving software quality prediction by noise filtering techniques. Journal of Computer Science and Technology, 22(3), 387-396.

Zhu X., Wu X., Chen Q. (2003, August): Eliminating class noise in large datasets. International Conference in Machine Learning (Vol. 3, pp. 920-927).

Examples

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# Next example is not run in order to save time
## Not run: 
data(iris)
# We fix a seed since there exists a random folds partition for the ensemble
set.seed(1)
out <- IPF(Species~., data = iris, s = 2)
summary(out, explicit = TRUE)
identical(out$cleanData, iris[setdiff(1:nrow(iris),out$remIdx),])

## End(Not run)