Add "histogram" to the possible aggregations of a Transform

[romainneutron]

Hello,

Given the Transform API documentation, we can not yet create a transform using Histogram as a pivot.aggregations.
This would be quite useful to store a Histogram value using histogram field type as a result of a transform.

Why?

When aggregating data, we can already compute percentiles for each result of the transform. However, If we need to compute a percentile aggregation on multiple lines of the transform-aggregated data, it's impossible because we need the data distribution to compute a percentile. Histograms are perfect for that.

Adding Histogram Transform aggregation would allow this using the value of the histogram field type.

Thanks

[elasticmachine]

Pinging @elastic/ml-core (Team:ML)

[hendrikmuhs]

Thanks for the feedback. I agree the histogram field type would be the way to go as output of a histogram aggregation in a transform, because for ordinary mappings we need to know the buckets in advance.