# Calculate the "phi coefficient" between two binary variables

### Description

The `phicoef`

function calculates the "phi coefficient" between
two binary variables.

### Usage

1 | ```
phicoef(x, y=NULL)
``` |

### Arguments

`x, y` |
Two logical vectors of the same length.
If |

### Value

The "phi coefficient" between the two binary variables. This is a single numeric value ranging from -1 to +1.

### Author(s)

H. Pagès

### References

http://en.wikipedia.org/wiki/Phi_coefficient

### Examples

1 2 3 4 5 6 7 8 9 10 | ```
set.seed(33)
x <- sample(c(TRUE, FALSE), 100, replace=TRUE)
y <- sample(c(TRUE, FALSE), 100, replace=TRUE)
phicoef(x, y)
phicoef(rep(x, 10), c(rep(x, 9), y))
stopifnot(phicoef(table(x, y)) == phicoef(x, y))
stopifnot(phicoef(y, x) == phicoef(x, y))
stopifnot(phicoef(x, !y) == - phicoef(x, y))
stopifnot(phicoef(x, x) == 1)
``` |

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