The regrid operator selects non-overlapping subarrays and performs aggregation on them.

Synopsis

regrid(array,grid_1 [, grid_2,...,grid_N],
           aggregate_call_1 [, aggregate_call_2,...,aggregate_call_N])

Summary

The regrid operator partitions the cells in the input array into blocks. For each block, regrid applies a specific aggregate operation over the value(s) of some attribute in each block.

Note that the chunk size does not have to be a multiple of the grid size, and the grids may span array chunks. However, processing is most efficient if chunk size is a multiple of the grid size, and grids do not span array chunks.

Inputs

The regrid operator takes the following arguments:

Example

To divide a 4×4 array into 4 equal partitions and calculates the average of each one, do the following. This process is known as spatial averaging.

1. Create an array m4x4:

   AFL% CREATE ARRAY m4x4 <val:double>[i=0:3; j=0:3];

   
   The output is:

   Query was executed successfully

2. Run this command, which increments val from 0 to 15:

   AFL% store(build (m4x4, i*4+j), m4x4);  

   
   The output is:

   {i,j} val
   {0,0} 0
   {0,1} 1
   {0,2} 2
   {0,3} 3
   {1,0} 4
   {1,1} 5
   {1,2} 6
   {1,3} 7
   {2,0} 8
   {2,1} 9
   {2,2} 10
   {2,3} 11
   {3,0} 12
   {3,1} 13
   {3,2} 14
   {3,3} 15

3. Regrid m4x4 into four (2*2) partitions and find the average of each partition.
   

   AFL% regrid(m4x4, 2,2, avg(val) as Average); 

   
   The output is:
   

   {i,j} Average
   {0,0} 2.5
   {0,1} 4.5
   {1,0} 10.5
   {1,1} 12.5

4. The regrid of 2x2 causes the following shape:

   0	1	2	3
   4	5	6	7
   8	9	10	11
   12	13	14	15

   and the averages are computed as:

   (0 + 1 + 4 + 5) / 4  = 2.5

   (2 + 3 +  6 + 7) / 4 = 4.5

   (8 + 9 + 12 + 13) / 4 = 10.5

   (10 + 11 + 14 + 15) / 4 =  12.5

   which results in:

   2.5	4.5
   10.5	12.5

   
   

5. Remove the m4x4 array

   AFL% remove(m4x4); 

   
   The output is:

   Query was executed successfully