The median aggregate returns the median from a set of input values. Available only in the Enterprise Edition.

Synopsis

AQL% SELECT median(attribute) FROM array;
AFL% aggregate(array,median(attribute),dimension_1[,dimension_2]...

Inputs

array: Specifies an array in the SciDb database.
median(attribute): Specifies which attribute to use when performing the median aggregation
dimension_n: Specifies which dimension to use when performing the median aggregation.

Library

The median aggregate resides in the Linear Algebra library. Run the following query to load this library:

AFL% load_library('linear_algebra');

Summary

The median aggregate returns the median from a set of input values. The median is the middle number (in a sorted list of numbers). The median value for a set of n values is defined as:

Example

To find the median of each column of a 3×3 matrix, do the following:

Load the appropriate library:

AFL% load_library('linear_algebra');

The output is:

Query was executed successfully

Create an array m3x3:

AFL% CREATE ARRAY m3x3<val:double>[i=0:2; j=0:2];

The output is:

Query was executed successfully

Store values 0–8 in the m3x3 array:

AFL% store(build(m3x3,i*3+j),m3x3);

The output is:

{i,j} val
{0,0} 0
{0,1} 1
{0,2} 2
{1,0} 3
{1,1} 4
{1,2} 5
{2,0} 6
{2,1} 7
{2,2} 8

Find the median of every column of m3x3 using the attribute val and the dimension j:
```
AFL% aggregate(m3x3,median(val),j);  
```
The output is:
```
{j} val_median
{0} 3
{1} 4
{2} 5 
```

Remove the m3x3 array:

AFL% remove(m3x3);

The output is:

Query was executed successfully

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