hash

Synopsis

hash(array)

Summary

This operator computes a distribution-independent parallelized hash signature of a SciDB array. The input can be any stored array name or AFL expression returning an array. The output is a 12-byte hash signature and a cell count as a dataframe.

Operator hash() has an avalanche property such that small changes to the input cause a large change in the result. For example:

AFL% hash(build(<val:string>[i=1:1], 'the quick brown fox'));
{inst,seq} data_hash,count
{0,0} '20e3e8e320e3e8e320e3e8e3',1

AFL% hash(build(<val:string>[i=1:1], 'The quick brown fox'));
{inst,seq} data_hash,count
{0,0} 'a2869654a2869654a2869654',1

For empty arrays, the returned hash is null and the returned count is 0.