1. A search retrieval system comprising: a search engine module employing a hardware processor for determining search results from searching documents stored from previous searches based on an inputted search term; and a clustering module employing the hardware processor for: forming a limited size hierarchy sortable data structure based on the search results from searching the documents stored from the previous searches; assigning a number of hierarchy locations for each search result in the hierarchy data structure; clustering the search results in the hierarchy data structure by assigning the search results to particular groups that are related based on proximity of each search result to one another, wherein proximity is one of hierarchical proximity and navigational proximity; selecting a user selectable hierarchy depth threshold via a user interface for selectively limiting a hierarchical depth of the clustered hierarchy data structure to adjust clustered hierarchical results for presentation according to the selected hierarchical depth threshold; and outputting the clustered hierarchical data structure as a list of search results that is adjusted for presentation based on the selected hierarchy depth threshold, wherein the clustering module assigns values to a portion of the hierarchy locations based on relative location of each of the search results to one another, and limits clustering results to a predefined number based on system capability and processing bandwidth.