Computes the average missing value gap of a vector.

`gapMiss(x, what = mean)`

- x
a numeric vector

- what
default is the arithmetic mean. One can include an own function that returns a vector of lenght 1 (e.g. median)

The gap statistics

The length of each sequence of missing values (gap) in a vector is calculated and the mean gap is reported

```
v <- rnorm(20)
v[3] <- NA
v[6:9] <- NA
v[13:17] <- NA
v
#> [1] 2.3307116 2.4220478 NA 0.9431652 0.5518939 NA
#> [7] NA NA NA -0.3524046 -0.9318654 0.4953990
#> [13] NA NA NA NA NA 2.3456733
#> [19] 1.6845347 1.1032059
gapMiss(v)
#> [1] 3.333333
gapMiss(v, what = median)
#> [1] 4
gapMiss(v, what = function(x) mean(x, trim = 0.1))
#> [1] 3.333333
gapMiss(v, what = var)
#> [1] 4.333333
```