## Arguments

vector |
A vector of numbers, or characters. Discrete probability of each item is calculated and the Shannon entropy is returned. |

## Value

Shannon entropy

Shannon entropy can be used as measures of gene expression
specificity, as well as measures of tissue diversity and
specialization. See references below.

We use `2`

as base for the entropy calculation, because in this
base the unit of entropy is *bit*.

## References

Martinez and Reyes-Valdes (2008) Defining diversity,
specialization, and gene specificity in transcriptomes through information
theory. PNAS 105(28):9709--9714

## Author

Jitao David Zhang <jitao_david.zhang@roche.com>

## Examples

```
myVec0 <- 1:9
entropy(myVec0) ## log2(9)
#> [1] 3.169925
myVec1 <- rep(1, 9)
entropy(myVec1)
#> [1] 0
entropy(LETTERS)
#> [1] 4.70044
entropy(rep(LETTERS, 5))
#> [1] 4.70044
```