1. A system comprising: one or more processors; one or more computer-readable storage mediums containing instructions configured to cause the one or more processors to perform operations including: analyzing, in a single-read pass, a distribution of time-stamped unstructured data to identify a plurality of potential time series data hierarchies for structuring the unstructured data, wherein a potential time series data hierarchy is a framework for structuring the unstructured data using time series; deriving, in the single-read pass, multiple structured time series from the unstructured data according to a selected time series data hierarchy, wherein the selected time series data hierarchy is selected from the plurality of potential time series data hierarchies; identifying, in the single-read pass, one or more user-specified time series analysis functions from a functions repository based on a function specification and the multiple structured time series, wherein the function specification describes the contents of the functions repository; generating, in the single-read pass, multiple updated structured time series using the identified time series analysis functions from the functions repository, wherein the updated structured time series is generated by applying the identified time series analysis functions to the multiple structured time series; and generating an output time series forecast corresponding to one or more of the multiple updated structured time series.