# Derivative Aggregation

A parent pipeline aggregation which calculates the derivative of a specified metric in a parent histogram (or date_histogram) aggregation. The specified metric must be numeric and the enclosing histogram must have min_doc_count set to 0 (default for histogram aggregations).

## Simple example

``````{
"aggs" : {
"sales_per_month" : {
"date_histogram" : {
"field" : "date",
"interval" : "month"
},
"aggs": {
"sales": {
"sum": {
"field": "price"
}
},
"sales_deriv": {
"derivative": {
"buckets_path": "sales"
}
}
}
}
}
}
``````

And now the query via DSL:

``````\$dateAggregation = new DateHistogramAggregation('sales_per_month', 'date', 'month');
\$sumAggregation = new SumAggregation('sales', 'price');
\$derivativeAggregation = new DerivativeAggregation('sales_deriv', 'sales');

\$search = new Search();

\$queryArray = \$search->toArray();
``````

## Second order derivative

Somewhat more complex would be an example of a second order derivatives. This functionality is presented in the folowing example:

``````{
"aggs" : {
"sales_per_month" : {
"date_histogram" : {
"field" : "date",
"interval" : "month"
},
"aggs": {
"sales": {
"sum": {
"field": "price"
}
},
"sales_deriv": {
"derivative": {
"buckets_path": "sales"
}
},
"sales_2nd_deriv": {
"derivative": {
"buckets_path": "sales_deriv"
}
}
}
}
}
}
``````

And now via DSL:

``````\$dateAggregation = new DateHistogramAggregation('sales_per_month', 'date', 'month');
\$sumAggregation = new SumAggregation('sales', 'price');
\$firstDerivativeAggregation = new DerivativeAggregation('sales_deriv', 'sales');
\$secondDerivativeAggregation = new DerivativeAggregation('sales_2nd_deriv', 'sales_deriv');