If you want to have universal method you”ll need an additional class: public class TreeItem<T> { public T Item { get; set; } public IEnumerable<TreeItem<T>> Children { get; set; } } Then use it with this helper: internal static class GenericHelpers { /// <summary> /// Generates tree of items from item list /// </summary> /// … Read more
one option if you don’t want to travel down the hierarchical data-set path, is to use a Nested Set (http://en.wikipedia.org/wiki/Nested_set_model). this allows you to store the entire collection in a single array (or list or whatever you want to call it) and use a “left” and “right” value to determine the structure and hierarchy of … Read more
Yes, this is possible, it’s a called a Modified Preorder Tree Traversal, as best described here Joe Celko’s Trees and Hierarchies in SQL for Smarties A working example (in PHP) is provided here http://www.sitepoint.com/article/hierarchical-data-database/2/
I’ve bookmarked this slidshare about SQL-Antipatterns, which discusses several alternatives: http://www.slideshare.net/billkarwin/sql-antipatterns-strike-back?src=embed The recommendation from there is to use a Closure Table (it’s explained in the slides). Here is the summary (slide 77): | Query Child | Query Subtree | Modify Tree | Ref. Integrity Adjacency List | Easy | Hard | Easy | Yes Path … Read more
MongoDB and CouchDB offer solutions, but not built in functionality. See this SO question on representing hierarchy in a relational database as most other NoSQL solutions I’ve seen are similar in this regard; where you have to write your own algorithms for recalculating that information as nodes are added, deleted and moved. Generally speaking you’re … Read more
pd.Grouper allows you to specify a “groupby instruction for a target object”. In particular, you can use it to group by dates even if df.index is not a DatetimeIndex: df.groupby(pd.Grouper(freq=’2D’, level=-1)) The level=-1 tells pd.Grouper to look for the dates in the last level of the MultiIndex. Moreover, you can use this in conjunction with … Read more
This requires a very basic recursive function to parse the child/parent pairs to a tree structure and another recursive function to print it out. Only one function would suffice but here’s two for clarity (a combined function can be found at the end of this answer). First initialize the array of child/parent pairs: $tree = … Read more
WITH q AS ( SELECT * FROM mytable WHERE ParentID IS NULL — this condition defines the ultimate ancestors in your chain, change it as appropriate UNION ALL SELECT m.* FROM mytable m JOIN q ON m.parentID = q.PersonID ) SELECT * FROM q By adding the ordering condition, you can preserve the tree order: … Read more
Store IDs of the objects in a hash table mapping to the specific object. Enumerate through all the objects and find their parent if it exists and update its parent pointer accordingly. class MyObject { // The actual object public int ParentID { get; set; } public int ID { get; set; } } class … Read more
For MySQL 8+: use the recursive with syntax. For MySQL 5.x: use inline variables, path IDs, or self-joins. MySQL 8+ with recursive cte (id, name, parent_id) as ( select id, name, parent_id from products where parent_id = 19 union all select p.id, p.name, p.parent_id from products p inner join cte on p.parent_id = cte.id ) … Read more