@Override
public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {
// Reset buffer so that it gets initialized with the current datatype of the column
buffer = null;
if (cachedResult == null) {
columnExp = (ColumnExpression) exps.get(0);
// Second exp will be a LiteralExpression of Boolean type indicating
// whether the ordering to be ASC/DESC
LiteralExpression isAscendingExpression = (LiteralExpression) exps.get(1);
boolean isAscending = (Boolean) isAscendingExpression.getValue();
// Third expression will be LiteralExpression
LiteralExpression percentileExp = (LiteralExpression) exps.get(2);
float p = ((Number) percentileExp.getValue()).floatValue();
Map<Object, Integer> sorted = getSortedValueVsCount(isAscending, columnExp.getDataType());
int currValue = 0;
Object result = null;
// Here the Percentile_disc returns the cum_dist() that is greater or equal to the
// Percentile (p) specified in the query. So the result set will be of that of the
// datatype of the column being selected
for (Entry<Object, Integer> entry : sorted.entrySet()) {
result = entry.getKey();
Integer value = entry.getValue();
currValue += value;
float cum_dist = (float) currValue / (float) totalCount;
if (cum_dist >= p) {
break;
}
}
this.cachedResult = result;
}
if (buffer == null) {
// Initialize based on the datatype
// columnExp cannot be null
buffer = new byte[columnExp.getDataType().getByteSize()];
}
// Copy the result to the buffer.
System.arraycopy(
columnExp.getDataType().toBytes(this.cachedResult), 0, buffer, 0, buffer.length);
ptr.set(buffer);
return true;
}
@Override
protected PDataType getResultDataType() {
return columnExp.getDataType();
}