Measure to compare two or more sets w.r.t. their similarity.

## Arguments

- sets
(

`list()`

)

List of character or integer vectors.`sets`

must have at least 2 elements.- p
(

`integer(1)`

)

Total number of possible elements.- na_value
(

`numeric(1)`

)

Value that should be returned if the measure is not defined for the input (as described in the note). Default is`NaN`

.- ...
(

`any`

)

Additional arguments. Currently ignored.

## Details

The Phi Coefficient is defined as the Pearson correlation between the binary representation of two sets \(A\) and \(B\). The binary representation for \(A\) is a logical vector of length \(p\) with the i-th element being 1 if the corresponding element is in \(A\), and 0 otherwise.

If more than two sets are provided, the mean of all pairwise scores is calculated.

This measure is undefined if one set contains none or all possible elements.

## References

Nogueira S, Brown G (2016).
“Measuring the Stability of Feature Selection.”
In *Machine Learning and Knowledge Discovery in Databases*, 442--457.
Springer International Publishing.
doi:10.1007/978-3-319-46227-1_28
.

Bommert A, Rahnenführer J, Lang M (2017).
“A Multicriteria Approach to Find Predictive and Sparse Models with Stable Feature Selection for High-Dimensional Data.”
*Computational and Mathematical Methods in Medicine*, **2017**, 1--18.
doi:10.1155/2017/7907163
.

Bommert A, Lang M (2021).
“stabm: Stability Measures for Feature Selection.”
*Journal of Open Source Software*, **6**(59), 3010.
doi:10.21105/joss.03010
.