Median
ordering-functions median
definition
The median of an attribute in the GeoDMS can be calculated with the rth_element function, with as second argument the value 0.5.
The median function in the GeoDMS calculates the middle value for each row of three given attributes. Thus median(a, b, c) :=
median(a, interval([min_elem](min_elem.html)(b, c), [max_elem](max_elem.html)(b, c))) :=
a < min_elem(b, c)
? min_elem(b, c)
: max_elem(b, c) < a
? max_elem(b, c)
: a
This can be used to bind a to a given range of allowed values.
syntax
- median(a, b, c)
conditions
- the domain arguments a, b, and c must match or be void.
- the values-unit of arguments a, b, and c must match.
- b is known to be not larger than c.
since version
since 2008
example
attribute<uint32> medianABC (ADomain) := median(A, B, C);
| A(int32) | B(int32) | C(int32) | medianABC |
|---|---|---|---|
| 0 | 1 | 2 | 1 |
| 1 | -1 | 4 | 1 |
| -2 | 2 | 2 | 2 |
| 4 | 0 | 7 | 4 |
| 999 | 111 | -5 | 111 |
| null | 0 | 0 | 0 |
| 0 | null | 0 | 0 |
| 0 | 0 | null | 0 |
| null | 0 | null | 0 |
| null | null | null | null |
ADomain, nr of rows = 10
In earlier versions (before 7.202) a null value in one of the arguments could result in a null value of the resulting data item. This now only occurs if all arguments have null values. This is a results of the implementation of min_elem and max_elem as functions that since then return the minimum defined value of each row.